Q & A on Teoretical ANalysis of Router Systems

Q: Simple IP routers have only one FIFO (First-in-first-out first-come-first-served) queue for the packets. That has the drawback that some users may achieve much higher data rate than others, for example if their packets are long in average, if their TCP sessions have long duration, and thus they avoid TCP slow-start, and if the IP packets only traverse a few routers. That is not fair. To address this problem, modern routers support fair packet scheduling algorithms, such as the Weighted Fair Queuing algorithm. This means that each flow (=stream=session) of IP packets has its own FIFO queue, instead of one common FIFO queue. If we only consider best-effort traffic (without QoS guarantees), then the router controls that backlogged flows (with at least on packet in queue) get equal bit rate, independently of packet sizes, TCP session durations, number of passed routers, etc. If we consider several routers, all flows do not achieve equal bandwith, but the minimum bandwith that a user can achieve is maximized. This is called max-min fairness. (I hope my terminology is correct.)

A flow is identified as a unique combination of source and destination IP address and TCP port number. This mean that a user who simultaneously communicates with N different hosts, or N different TCP ports, will achieve N times higher data rate than a user who communicates with only one host and one TCP port. I.M.O., that is not fair. I think that if several packets goes to [from] the same IP host, and that host is situated in the same (sub)net as the IP router, then they should be considered as the same flow irrespectively of the source [destination] and the TCP port numbers. I haven't seen any discussion about it in scientific papers, or in CISCO knowledge database, so I guess that CISCO routers do not support this. Do you have some idea why?

In the academic world, a lot of other fair resource sharing algorithms are studied, such as deficit round robin, and algorithms for proportional fairness. Do you know if these algorithms are supported by routers existing on the market today?

A: You are correct that the academic world is overrun with theoretical studies of packet scheduling and traffic engineering. Researchers in the area of Performance Evaluation have had little impact in operating systems and databases; now they are applying the same techniques to networks. In fact, everyone I know who used to write papers on performance of something is now writing papers on performance of networks. Recently, I had a visitor in my office who told me he was shocked to discover that the academic work was almost completely ignored by industry -- engineers bulding switches and routers didn't find that the analysis worked in practice.

So, you are discussing a few details, when the important question is whether the whole scheme is worthwhile. Many of us in networking think that it is not -- scheduling will NEVER be a satisfactory solution to the resource problme. The notion of ``equal pain'' didn't work for operating systems, doesn't work for automobile traffic, and it won't work for networks. The only viable long-term solution is increasing resources (the ``big bandwidth'' solution).

Q & A on Application Level Gateways,

Q: Please could you help me understand this - how do application (level) gateways work?

A: An application gateway is a running program that connects two or more (heterogeneous) distributed systems. For example, one type of application gateway is used to connect heterogeneous e-mail systems. To understand the motivation, assume that you work for a company that runs proprietary e-mail software internally. If the company wants to send e-mail across the Internet, it must format the message according to the Internet standard and must use standard Internet protocols to transfer the messahe. An application gateway can be placed between the two -- the gateway accepts outgoing mail in the proprietary format, reformats it to use the Internet standard, and sends it. Similarly, the application gateway accepts all incoming e-mail, reformats it to use the proprietary system, and forwards each message to the appropriate recipient using the proprietary e-mail system.

Q: How are they related to ip packet filtering.

A: Application gateways are seldom used to perform packet filtering because the overhead is high (each packet must be transferred from inside the operating system to the application gateway and back into the operating system for transmission, and there is usually a context switch as well). Thus, most packet filtering is performed by a router or by protocol software inside an operating system.

Q & A on Ethernet Transceivers and "10BaseT",

Q: I had a few questions regarding ethernet ..

Unlike thicknet, thinnet and twisted pair do not have a explicit transceiver - dont they require one or it is in the NIC(for thinnet) or hub for twisted pair

A: You are correct, thinnet and twisted pair do not have an external transceiver. The necessary transmission hardware is part of the network interface card (NIC) for thinnet. In twisted pair Ethernet, the hub contains active electronics that can amplify and retransmit signals. Thus, the NIC in a given computer only needs to propagate the signal as far as the hub.

Q: Why is 10Base-T called so

A: The "10" stands for the transfer rate of 10 megabits per second. The "T" stands for twisted pair. Thicknet, which has a maximum cable segment length of 500 meters, is named 10Base-5, and thinnet, which has a maximum cable length of 200 meters is named 10Base-2. (Note: the names can be written without the dash).

Q: In Twisted pair - we refer to the logical topology as a BUS but the physical topology is Star - have I got it right.

A: Yes. The original Ethernet was, of course, both a physical and logical bus -- a single cable comprised the medium over which signals were transmitted. From the point of view of an attached computer, twisted pair Ethernet appears logically to be exactly the same as a single cable (i.e., twisted pair Ethernet uses CSMA/CD for media access just like the original Ethernet). Physically, however, twisted pair Ethernet consists of a hub to which each computer connects, making it a physical star. One often hears the terms "star-shaped bus" or "bus-in-a-box" used to describe the configuration.

Q: Why is that the hosts on the ethernet need to be seperated by a minimum distance (3m?). I understand the need for maximum distance.

A: This answer from Tim Korb:

It's in 7.6.2 of the spec. The placement is to reduce signal reflections and, in particular, to make sure that placement does not "add in phase to a significant degree". The spec is not to insure a minimum distance, but to insure regular placement. The placement distance, incidentally, is 2.5 meters.

Q & A on 100BaseT and 10BaseT Cabling,

Q: Can 100-Base-T ethernet cables be used with 10-Base-T cables? In which case, some pairs are just ignored?

A: There are two parts to the answer. First, as long as the cable meets the standard (i.e., category 5), the same type of cable can indeed be used for either. Second, twisted pair Ethernet uses RJ-45 connectors (8-pin modular connectors that are larger versions of 4-wire connectors used on a conventional telephone). As long as all eight wires are connected, the same connector can be plugged into either 10 or 100 Mbps equipment.

As a practical matter, most network interface cards are now called ``10/100 cards'' because the hardware automatically senses whether it has been connected to a 10Base-T hub or a 100Base-T hub. The same cable can be used between the computer and the hub in each case. In our lab, for example, when we ask students to measure 10 and 100 Mbps Ethernet, they switch computers from one to the other merely by changing the hub -- the same cable is used.

Q & A on One LAN or Many LANs on a Campus,

Q: I have a question about LANs. Are computers on a large university campus on one LAN or many LANs?

A: In general one LAN is incapable of supporting an entire large campus. As a general rule, each LAN is limited to an area approximaely the size of a single building. Indeed, mnay large unoversity buildings have more than one LAN. There are exceptions, of course, but you can use that as a guideline.

Q: Is it right that Ips with same mask are on a same LAN?

A: "Ips" is not a valid technical term. I assume you mean IP addresses (the 32-bit value assigned to a host on an internet). If so, the answer is "no". It's not the mask itself that determines whether two computers are on the same network, but whether the prefixes of the two addresses match. The mask simply tells where the prefix ends.. For example, the network in the Xinu lab here at Purdue and the main CS departmental network both use the same mask:

255.255.255.0

However, the prefixes differ in the third octet. Thus, two hosts on those two networks might have addresses:

128.10.2.1

and

128.10.3.1

When the mask is applied (logical and), the resulting prefixes are

128.10.2.0

and

128.10.3.0

which differ. However, the following two addresses are on the same network because when the mask is applied, both addresses have prefix 128.10.2.0

128.10.2.26

and

128.10.2.3

Q & A on ICMP and UDP "ping",

Q: Touching the subject "source for ping" I think that could be useful to cite an article of Eric T. Horne, published by SysAdmin in the July/August 1993 issue, where he shows the source code for a newping that uses the TIME/TCP port, instead of the traditional ICMP, to detect CPU activity for the destination machine. I hope this citation be useful.

A: Actually, one doesn't need to use the time port because both TCP and UDP have a standard port reserved for echo: port 7. A program called ``upds'' has been floating around for many years that uses the UDP echo port exactly like ping uses ICMP echo. In fact, when I lecture to professional audiences, I usually talk about udps and explain that unlike ping, it determines more than whether interrupts are working on the remote computer.

Q & A on Netweork Analyzer Software,

Q: I am planning to use your book, Computer Networks and Internets, for my class (Computer Networks) in the coming Fall semester. As you wrote in the preface that students seem to understand more on the material if they see packets on a real network. You also mention about an inexpensive network analyzer software. Would you please give me the name of the network analyzer software that good but not too expensive? The department cannot afford to by an expensive HP network anlyzer.

A: Here at Purdue, we have used a variety of network analyzer software running on a workstation (i.e., a PC) rather than a dedicated box. Currently, we're using 'snoop' (a program available with Solaris); we used to use 'etherfind'. To make it 'safe' for undergrads, we (1) install an extra NIC in each workstation that connects to an experimental network, and (2) use the sudo program to invoke snoop, which restricts what the students are allowed to do.

I should tell you that, it's not difficult to roll your own -- as a first project in my graduate-level internetworking course, I have each student build an analyzer (put the interface card in promiscuous mode and selectively dump packets).

Q: I totally agree with you that teaching computer network, the lab is a must. Your book is very good, you make something so complex to be simple.

A: Thanks.

Q: I will teach this course for one-semester, what Parts should I cover? Part 1 through 3 as you suggested in the preface?

A: I'm currently teaching a senior-level networking course from the text, with the following empahsis:

• 1.5 weeks : Introduction, signals, media, bandwidth, throughput, snd multiplexing

• 5.0 weeks: Packet transmission concepts and technologies; LANs, WANs, and local loop technologies

• 5.0 weeks: Internetworking fundamentals and internals
• 3.0 weeks: Internet applications

Q & A on Writing a Network Analyzer,

Q: I'm interested in exploring the idea of writing one's own analyzer. What do you use for this, the Berkeley packet library?

A: The grad students use my operating system, Xinu. We give them a device driver that can put the NIC in promiscuous mode to receive packets; they build the rest inside the kernel. Undergrads use snoop to capture frames, put them in a file, and then decode them offline (there are packet traces on the CD-ROM that comes with the book if you want to try decoding headers but don't have direct access to the driver).

Q: Also, I've just recently become more interested in networking, and I'm pretty much teaching myself this stuff. I was wondering what kind of approach you'd recommend for this type of education. I've read your TCP/IP Volumes I and III, as well as the RFCs for TCP,IP,ICMP. It's a bit of a curve, but once you read a few you want to read them all. I enjoy just reading the specs. What I guess I really need is a big project.

A: Yes, the only way to really appreciate the subtleties is to build. You can do packet analysis to find out about header details of existing protocols or watch traffic, but I suggest trying to implement a reliable protocol. If you don't have low-level facilities available, start with UDP -- build your own protocol and use UDP as a 'delivery' mechanism. Then, place an intermediate application between the two sides that delays, reorders, duplicates, or purposefully damages a few bits. See if you can design a protocol that detects/corrects the problem.

Q & A on Interpreting IP Addresses in Octal,

Q: Recently, I got a IP address for my computer in one of my university's resident halls. The address is read as xxx.xxx.xxx.070. So I did a ping to this address (just want to make sure it's not used by other people since I haven't connected my machine) and found out the machine already exists. When I did a telnet, I was really connected to a machine. By looking more carefully, I found I was connected to xxx.xxx.xxx.56 instead. What is the explanation?

A: Understanding the mystery requires you to know several facts:

1) 56 in decimal is 70 in octal (base 8).

2) The C programming language (and UNIX programs in general) follow the convention of interpreting constants with a leading zero as being an octal number.

3) Many TCP/IP programs such as ping and telnet that accept a dotted decimal address as an argument follow the C conventon.

I suppose that someone who was unaware that software could be confused by leading zeroes chose to represent 70 as 070 when they handed out your address. They probably thought it would make the printed version look nicer...

Q & A on New Top-Level Domains for DNS,

Q: I thought the elaborated domain name set (most significant segment list) shown in Figure 26.1 (p. 367) of the 2nd ed. had not received final approval and therefore was not (yet) in use. Did I miss a post on this and am I mistaken? Please advise as to the status of this.

A: Well... I made a bad call on this one. While I was revising the text last Spring, the new list was being considered. I each a tutorial with Paul Mockapetris (the guy who invented DNS), and he thought adoption had high probability. So, I gambled that it would be in place by now.

But... as far as I can tell, there's been no formal action yet. Furthermore, with the untimely death of Jon Postel, many things are changing, including the imminent creation of the Domain Name Service Organization.

I'll add this item to the errata.

Q & A on WAP and TCP.

Q: I would like to know why is that why WAP doesn't use TCP?

A: WAP (Wireless Access Protocol) isn't a transfer protocol like HTTP. Instead, it's a complete protocol stack. Although WAP doesn't rule out using TCP, the main focus is on handheld devices:

1) WAP is intended to run over existing protocols that have been developed for delivering data across the cellular telephone system (e.g., CDPD).

2) WAP is optimized for delivery channels that have low bandwidth.

If reliability is needed, the Wireless Session Protocol (WSP) component of the WAP stack must provide it.

Q & A on TCP Segment Lengths.

Q: I have a couple of quick questions regarding the TCP protocol.

1. When I checked the TCP segment format, as shown in fig 22.6 of your Computer Networks and Internets book, I did not find any field in the header to indicate the segment length. And the question is: - How does the IP protocol in the same host know the length of the segment?

A: The length is not stored in the header. However, when TCP manufactures a segment, it passes the length (and other information) to IP along with the segment.

Q: - Also, how does the TCP protocol in the other side know the length of the segment?

A: When IP receives a datagram carrying TCP, IP computes the length of the segment (from the IP header length and total datagram length), and then passes the length to TCP along with the segment.

Q: 2. As far as I know, a TCP segment will be sent to IP to transfer it to the other side. The TCP header only has DESTINATION PORT in its header, which is just 16 bits. From where the IP protocol will know the IP address of the destination/source?

A: The IP destination address is among the additional information that TCP must pass to IP along with an outgoing segment.

Q: As far as I know, the application layer knows about the ``connection'' and its two endpoints. However, there is no direct link between the application layer and the IP layer. That is why, I am asking my question.

A: There must be an Application Program Interface (API) that allows the application to specify details such as the IP address and protocol port number of a remote site. Once the information has been specified, protocol software has access to it.

Q & A on TCP/IP Between Hosts on a Single Network.

Q: I just wanted to know if TCP/IP is required when the client and the server are located on the same physical network.

A: If the operating systems on the two computer provide support for some other suite (or direct access to the underlying network), TCP/IP is not required. In practice, however, chances of being able to use an alternative are extremely slim -- no protocols are available on as many computer systems as TCP/IP, which has become the universal language of networking.

Q & A on "Internetworking with TCP/IP, Volume 1".

Q: What is the title of this book (Volume 1 of Internetworking with TCP/IP)?

A: The book to which I referred is:

 D. Comer,  Internetworking With TCP/IP Volume 1: Principles,
 Protocols, and Architectures, 3rd edition, Prentice Hall, 1995.
 ISBN 0-13-216987-8

You can find a list of all my books on my Web page:

 http://www.cs.purdue.edu/people/comer

Q & A on TPC/IP Layering Model,

Q: why does the book, at pp. 230, show that the TCP/IP has 5 layers, while other books (e.g., Tanenbaum's and Hunt's books) say it is 4 layers? Is it network interface layer and physical layer?, or is it host-to-network layer?

A: When I wrote Volume 1 of Internetworking with TCP/IP, I was on the IAB working with the researchers who created the protocols. I documented what they had created: a 5-layer model. Furthermore, I used the names we commonly used for the layers (e.g., network interface layer). Since then, other authors have tried to rephrase the model (e.g., at least one author omits the hardware layer). I suppose they hope such changes will increase sales of their books.

Q & A on IP Address Prefixes and Suffixes

Q: Our class had a question about table 16.13 on page 245 (2nd edition).

The headers in the table are "prefix" and "suffix", implying that these address the bits AFTER the bits identifying the address class.

A: When I use the term ``prefix'', I include the bits that identify the class as well as bits that identify network.

Q: We had a question about the entries for "this computer" and "limited broadcast". Is this really referring to the prefix (where self-identifying bits for address class are still used), or are all octets in the address 0's or 1's.

A: The address labeled ``this computer'' consists of all 32 zero bits, and the address for ``limited broadcast'' consists of all 32 one bits. The class bits are not interpreted in these special addresses.

Q & A on "Net 0" IP Addresses.

Q: Is it Ok to assign 0.xx.xx.xx to an IP host number, where xx != 0, i.e., class A with a prefix = all-0s and suffix is any thing, but not all-0's.

A: The question doesn't need an asnwer: addresses on the Internet are assigned by a central authority, so the question is irrelevant. Addresses on private networks are assigned to avoid global addresses (e.g., the IETF recommends using the class A address 10.0.0.0, which will never again be assigned to any network in the Internet). Thus, one would never assign 0.x.x.x in either case.

Q: But according to Tanenbaum, pp. 417, he said that when a prefix is all-0s and suffix is HOST, it means a host on this network. He added, these addresses allow machines to refer to their own network without knowing its number, but they have to know its class to know how many 0s to include.

A: That doesn't make sense. One cannot know the ``class'' of the local network address without knowing the address.

Q: This means, according to Tanenbaum, that 0.xx.xx.xx is a special address. However, I did not find it listed as a special address in Figure 16.7. That is why I got confused about this address.

A: There's no point in worrying about it because it's not used that way in practice.

Q: With reference to:

Is it Ok to assign 0.xx.xx.xx to an IP host number, where xx != 0, i.e., class A with a prefix = all-0s and suffix is any thing, but not all-0's.

Would it be a simple case of xx != 0? (Even with an ordinary class A prefix: 40.0.0.8) Obviously not all zeros, but some zeros are permitted.

A: I understood the question to be whether it was permissible to use the Class A prefix that consists of eight zero bits. At least some of the host part (the last three octets) will be nonzero, but that doesn't answer the question of whether Class A prefixes start at 0 or 1.

Q & A on Network Standard Byte Order and User Data.

Q: I can understand the neccessary of the internet standard for byte order. But, why the user data field in packet is exempt from the standard?

If i communicate between a Little Endian machine and a Big Endian machine, the data would be misunderstand or my program must deal with the byte order, which means that my program is related to the unique machine, right?

A: You are correct in asserting that all data must be translated. If an application running on a Little Endian computer merely transfers a copy of the bits of an integer to an application running on a Big endian computer, the receiver will interpret the value of the bits differently, resulting in an error.

However, it does not make sense for network protocol to require translations because only the application programmer understands the data being sent across the network. If an application uses non-numeric data or has a reason to specify a particular representation, the network protocols should not interfere.

As a result, application programmers have complete freedom to choose a data representation, but also have the responsibility to handle any byte-order conversions or their clients and servers will not work correctly when communicating between two computers that have different native byte orders.

Q & A on Network Topologies,

Q: 1) Can a ring topology be used on Ethernet? If yes, how?

A: No, Ethernet uses a bus topology.

Q: 2) Would a pure ring or a star ring topology be easier to maintain and troubleshoot? Why?

A: Is this a homework problem?

Q: 3) What is the maximum distance (in meters and feet) a node can be from a hub without any repeaters in between?

The nominal length of a twisted pair segment is 100 meters; slightly longer wiring *may* work, depending on the amount of electrical noise in the environment and the exact type of cable.

Q & A on Code for Internetworking with TCP/IP, Volume 3

Q: In your book, (sorry forget the title -Networking with TCP/IP?) Volume III, is the example code for client and server available on the Internet for download?

A: All the code from my books is available for download. Volume 3 comes in three versions that use slightly different interfaces: Sockets, TLI, and Windows sockets. The easiest way to obtain the code is from the following Web page which has a link to the code for each networking book:

Q & A on Attenuation in Ethernet Network Design

Q: Another reason for maximum bus segment length it that there is more attenuation and more noice on a long cable, and therefor more bit errors, but I don't think that that is the main reason.

A: Yes, attenuation is a minor design issue -- for a given transmitter power level and type of cable, the signal will only reach a certain distance before becoming too weak to receive realiably. However, if attenuation were a major limitation issue, it could be overcome by more stringent cable requirements or increased transmitter power levels.

Q & A on Hardware Technologies

Q: CNAI, p.32D. Does the fact that Ethernet uses CSMA/CD preclude an Ethernet system from using frequency division multiplexing? That is, does the existence of one carrier wave on the ether keep every other host off?

A: Yes. When one host is transmitting on a segment (or a hub) other hosts refrain from transmitting. You can imagine that they all use the same "frequency". Thus, there is no FDM.

Q: Is X25net a connection oriented technology?

A: Yes. Like ATM, X.25 is connection-oriented.

Q: When you state that ' "tunneling" treats packets like data' do you mean this technique treats packets like a continuous stream of data where individual packets are sent contiguously, one after another?

A: Technically, the difference between *tunneling* and *encapsulation* is that encapsulation sends datagrams over hardware frames, while tunneling sends datagrams over some "higher level" protocol system. In terms of X.25 the term *tunneling* is appropriate because X.25 adds several layers of protocols on top of the underlying hardware.

Whether the interface is stream-oriented or message-oriented is completely independent of the underlying transmission scheme (e.g., TCP offers a stream-oriented interface, but sends data in individual segments, with one segment per datagram). Thus, one can tunnel over a stream-oriented interface or a message-oriented interface.

Q: LAN's vs. WAN's. Can the nodes of a LAN be a subset of the nodes of a WAN (or are they disjoint sets)? Are WAN's ever aggregates of LAN's?

A: The quick answer is that because LANs and WANs use completely different technologies, one cannot build a WAN by aggregating LANs. However.... some WAN technologies provide an interface that *appears* to be a LAN. For example, if one leases a satellite channel between San Francisco and new York, the equipment might appear as an Ethernet bridge to the computers using it. That is, a computer in San Francisco plugs into a 10BASE-T port, and appears to send and receive Ethernet frames. The bridge takes each transmitted frame, encodes it for transmission, sends the result across the satellite channel to New York, which then decodes the frame and delivers it to a 10BASE-T port. The advantage of using a 10BASE-T interface is that the attached computers can use standard hardware and software. That doesn't mean there's an Ethernet underneath (i.e., it's only the interface that appears to be an Ethernet). By the way, the same is true of ISDN and DSL technologies -- they accept and deliver Ethernet frames.

Q: Is it correct that a computer (host or router) has a physical address, but that its _connection_ to the Internet has an IP address? Or--is the physical address actually associated with the connection also?

A: Every network interface card has a physical address. If a computer connects to more than one network, it has more than one physical address. Thus, a router *always* has multiple physical addresses.

Q: Is the mapping from IP addresses to physical addresses one-to-one? In particular, if a host is multi-homed with two IP addresses, must it also have two physical addresses?

A: In almost all real internets the mapping is one-to-one. People sometimes play games where they assign *more* than one IP address to a given hardware interface (e.g. to simulate two subnets on the same physical wire). These many-one configurations fall outside the original intended use of IP. :-)

Q: In volume I you assert that routers must choose between routes employing physical networks that have properties of delay, throughput, and reliability. How do routers actually store this information? Is there some kind of static evaluation function the output of which characterizes the 'goodness' of a prospective route?

A: Although there has been much research on routing, the real Internet usually chooses the route that minimizes the hop count. Thus, the *type of service* routing field in the IP header is seldom used and the type of service routing you describe is seldom implemented. If it were, routers would need to keep detailed information about the throughput and delay along all paths. Delay changes so quickly that keeping accurate information is impossible.

Q: You state that each hardware technology imposes its own upper bound (MTU's) on frame size (e.g., Ethernet 1500, FDDI around 4K). Are all frames emanating from a given host 'A' of exactly the same size all the time? Do all hosts attached to Ethernet nets send frames of size 1500?

A: No, in most technologies, a frame is only as large as needed. For example, if you need to send 200 octets across an Ethernet, the outgoing frame will have a header followed by exactly 200 octets of data. For example, if a 600-octet datagram is sent over an Ethernet, the resulting frame has 600 octets of data following the Ethernet header.

As a practical matter, TCP/IP tries to optimize efficiency. Thus, if you use TCP/IP to transfer a file across an Ethernet, IP will create datagrams that are each 1500 octets long.

Another technical point: some technologies require a minimum frame size (so the hardware can distinguish real frames from a small burst of electrical noise or so the MAC protocols function properly). For example, Ethernet requires a frame to contain at least 64 octets of data. If the data being sent is less than the minimum size, it must be padded (e.g., with zeroes).

By the way, if a technology sends packets of a fixed size, they are called *cells*, not *frames*. For example, because each packet sent by ATM is the same size (53-octets), they are called *cells*, and ATM is known as a *cell-switching technology*.

Q: Please verify: when a host sends datagrams, they can be of *varying* size, but the frames emanating from the host will always be the same size.

A: Not correct -- both datagrams and frames can be of *varying* size.

Q: Are there actually two routing algorithms employed for forwarding data: one for frames on the physical net and one for datagrams on the virtual net?

A: In most LAN technologies, there is no "routing" -- one sends the packet across the LAN, all computers receive the frame, and all interface cards except the intended destination discard the frame. In most WAN technologies (at least the WANs that connect multiple hosts), the WAN needs to route frames among the switches that make up the WAN. Thus, when you send a packet across an X.25 network, switches inside the network route the packet from the port where it entered the network to the port where it exits.

So, the general answer is that routing occurs only at the IP level, not at the physical net (a handful of WAN technologies being the exception).

Q: Bridges vs. Routers: Can a bridge attach two different types of LAN's say, an Ethernet and a CDDI? How about an Ethernet and an FDDI?

A: In general, no. Bridges do not change the *shape* of the frame or the addresses. Thus, the technologies must have compatible frame formats and compatible addressing schemes. Thus, one could bridge CDDI and FDDI, but could not bridge Ethernet and FDDI.

Computer Network Questions and Answers Part 1

Can you be able to identify between Straight- through and Cross- over cable wiring?
Straight-through is type of wiring that is one to to one connection Cross- over is type of wiring which those wires are got switchedWe use Straight-through cable when we connect between NIC Adapter and Hub. Using Cross-over cable when connect between two NIC Adapters or sometime between two hubs.

What is the significance of the IP address 255.255.255.255?
The limited broadcast address is utilized when an IP node must perform a one-to-everyone delivery on the local network but the network ID is unknown.

What tool have you used to create and analyze packet captures?
Network Monitor in Win2K / Win2K3, Ethereal in Linux, OptiView Series II (by Fluke Networks).

What is LDAP used for?
LDAP is a set of protocol used for providing access to information directories.

What is the difference between a domain local group and a global group?
Domain local groups grant permissions to objects within the domain in which the reside. Global groups contain grant permissions tree or forest wide for any objects within the Active Directory

How do you set a default route on an IOS Cisco router?
ip route 0.0.0.0 0.0.0.0 x.x.x.x [where x.x.x.x represents the destination address]

What is a default gateway?
The exit-point from one network and entry-way into another network, often the router of the network.

What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.

What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.

What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side

Computer Network Questions and Answers Part 2.

What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.

What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.

What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.

What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.

What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

What is LLC?
LLC is Logical Link Control, one of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router

What is MAU?
In token Ring , hub is called Multistation Access Unit(MAU).

Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.

What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.

Computer Network Questions and Answers Part 3.

What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255

What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.

What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.

What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).

Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
Baud rate = bit rate / N ?: where N is no-of-bits represented by each signal shift.

How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats.

What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.

What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.

What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.

Computer Network Questions and Answers Part 4.

What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.

What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.

What do you meant by “triple X” in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called “triple X”.

What is SAP?
SAP: Service Access Point , Series of interface points that allow other computers to communicate with the other layers of network protocol stack.

How does the browser know to go to a certain IP address when you enter a domain like crackthecampus.com?
It searches through local DNS cache, if nothing is there, it queries the ISP’s DNS server

What is Load balancing?
If the number of incoming clients requests exceeds the number of processes in a server class, the TP Monitor may dynamically start new ones and this is called Load balancing

What is OLTP?
In the transaction server, the client component usually includes GUI and the server components usually consists of SQL transactions against a database. These applications are called OLTP (Online Transaction Processing) OLTP Applications typically,
Receive a fixed set of inputs from remote clients. Perform multiple pre-compiled SQL comments against a local database.Commit the work and Return a fixed set of results.

What is Message Oriented Middleware (MOM)?
MOM allows general purpose messages to be exchanged in a Client/Server system using message queues. Applications communicate over networks by simply putting messages in the queues and getting messages from queues. It typically provides a very simple high level APIs to its services.
MOM’s messaging and queuing allow clients and servers to communicate across a network without being linked by a private, dedicated, logical connection. The clients and server can run at different times. It is a post-office like metaphor.

What is meant by Asymmetrical protocols?
There is a many-to-one relationship between clients and server. Clients always initiate the dialog by requesting a service. Servers are passively awaiting for requests from clients.

What is Groupware server?
Groupware addresses the management of semi-structured information such as text, image, mail, bulletin boards and the flow of work. These Client/Server systems have people indirect contact with other people.

Computer Network Questions and Answers Part 5,

What is Client/Server?
Clients and Servers are separate logical entities that work together over a network to accomplish a task. Many systems with very different architectures that are connected together are also called Client/Server.

What is a File server?
File servers are useful for sharing files across a network. With a file server, the client passes requests for file records over nerwork to file server.

What are called Fat clients and Fat servers?
If the bulk of the application runs on the Client side, then it is Fat clients. It is used for decision support and personal software.
If the bulk of the application runs on the Server side, then it is Fat servers. It tries to minimize network interchanges by creating more abstract levels of services.

What is Remote Procedure Call (RPC)?
RPC hides the intricacies of the network by using the ordinary procedure call mechanism familiar to every programmer. A client process calls a function on a remote server and suspends itself until it gets back the results. Parameters are passed like in any ordinary procedure. The RPC, like an ordinary procedure, is synchoronous. The process that issues the call waits until it gets the results.
Under the covers, the RPC run-time software collects values for the parameters, forms a message, and sends it to the remote server. The server receives the request, unpack the parameters, calls the procedures, and sends the reply back to the client. It is a telephone-like metaphor.

What are the building blocks of Client/Server?
The client ,The server and Middleware.

What is a TP Monitor?
There is no commonly accepted definition for a TP monitor. According to Jeri Edwards’ a TP Monitor is “an OS for transaction processing”.
TP Monitor does mainly two things extremely well. They are Process management and Transaction management.
They were originally introduced to run classes of applications that could service hundreds and sometimes thousands of clients. TP Monitors provide an OS - on top of existing OS - that connects in real time these thousands of humans with a pool of shared server processes.

What are Super servers?
These are fully-loaded machines which includes multiprocessors, high-speed disk arrays for intervive I/O and fault tolerant features.

What is a Web server?
This new model of Client/Server consists of thin, protable, “universal” clients that talk to superfat servers. In the simplet form, a web server returns documents when clients ask for them by name. The clients and server communicate using an RPC-like protocol called HTTP.

What is a Database Server?
With a database server, the client passes SQL requests as messages to the database server. The results of each SQL command are returned over the network. The server uses its own processing power to find the request data instead of passing all the records back to the client and then getting it find its own data. The result is a much more efficient use of distributed processing power. It is also known as SQL engine.

What is an Object server?
With an object server, the Client/Server application is written as a set of communicating objects. Client object communicate with server objects using an Object Request Broker (ORB). The client invokes a method on a remote object. The ORB locates an instance of that object server class, invokes the requested method and returns the results to the client object. Server objects must provide support for concurrency and sharing. The ORB brings it all together.

Computer Network Questions and Answers Part 6.

What is anonymous FTP and why would you use it?
Anonymous FTP enables users to connect to a host without using a valid login and password. Usually, anonymous FTP uses a login called anonymous or guest, with the password usually requesting the user’s ID for tracking purposes only. Anonymous FTP is used to enable a large number of users to access files on the host without having to go to the trouble of setting up logins for them all. Anonymous FTP systems usually have strict controls over the areas an anonymous user can access.

What is a DNS resource record?
A resource record is an entry in a name server’s database. There are several types of resource records used, including name-to-address resolution information. Resource records are maintained as ASCII files.

Explain the function of Transmission Control Block
A TCB is a complex data structure that contains a considerable amount of information about each connection.

What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.

What protocol is used by DNS name servers?
DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a connectionless protocol offers. Of course, transmission reliability suffers with UDP.

What is External Data Representation?
External Data Representation is a method of encoding data within an RPC message, used to ensure that the data is not system-dependent.

What is Brouter?
Hybrid devices that combine the features of both bridges and routers.

Explain 5-4-3 rule.
In a Ethernet network, between any two points on the network, there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.

What is REX?
Request to Exit (REX) - A signal that informs the controller that someone has requested to exit from a secure area.

What are major types of networks and explain?
Server-based network.
Peer-to-peer network.
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration.

Computer Network Questions and Answers Part 7.

Explain the importance and use of each, Version, Culture and PublicKeyToken for an assembly.
This three alongwith name of the assembly provide a strong name or fully qualified name to the assembly. When a assebly is referenced with all three.
PublicKeyToken: Each assembly can have a public key embedded in its manifest that identifies the developer. This ensures that once the assembly ships, no one can modify the code or other resources contained in the assembly.
Culture: Specifies which culture the assembly supports
Version: The version number of the assembly.It is of the following form major.minor.build.revision.

How you will set the datarelation between two columns?
ADO.NET provides DataRelation object to set relation between two columns.It helps to enforce the following constraints,a unique constraint, which guarantees that a column in the table contains no duplicates and a foreign-key constraint,which can be used to maintain referential integrity.A unique constraint is implemented either by simply setting the Unique property of a data column to true, or by adding an instance of the UniqueConstraint class to the DataRelation object’s ParentKeyConstraint. As part of the foreign-key constraint, you can specify referential integrity rules that are applied at three points,when a parent record is updated,when a parent record is deleted and when a change is accepted or rejected.

What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.

What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.

What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.

What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet’s topology to make accurate routing decisions.

What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).

What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.

What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system

Computer Network Questions and Answers Part 8.

What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols

What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.

What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.

What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.

What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions

What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.

What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router

Computer Network Questions and Answers Part 9,

What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).

What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

What are the important topologies for networks?
BUS topology:In this each computer is directly connected to primary network cable in a single line.
Advantages:Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:In this all computers are connected using a central hub.
Advantages:Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:In this all computers are connected in loop.
Advantages:All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it

What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.

What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.

What are the different type of networking / internetworking devices?
Repeater:Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges: These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.

What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.It consists of the following:
802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used.
The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.

What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
a)Guided Media:These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.

What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth

Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.

networking 146

What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.

What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.

How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats

What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.

What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.

What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.

What is IP?
IP is Internet Protocol. It is the network protocol which is used to send information from one computer to another over the network over the internet in the form of packets

What’s the meaning of ARP in TCP/IP?
The “ARP” stands for Address Resolution Protocol. The ARP standard defines two basic message types: a request and a response. a request message contains an IP address and requests the corresponding hardware address; a replay contains both the IP address, sent in the request, and the hardware address.

What is data link layer in the OSI reference model responsible for?
Data link layer is located above the physical layer, but below the network layer. Taking raw data bits and packaging them into frames. The network layer will be responsible for addressing the frames, while the physical layer is reponsible for retrieving and sending raw data bits.

What is binding order?
The order by which the network protocols are used for client-server communications. The most frequently used protocols should be at the top.

How do cryptography-based keys ensure the validity of data transferred across the network?
Each IP packet is assigned a checksum, so if the checksums do not match on both receiving and transmitting ends, the data was modified or corrupted.

What is UTP?
UTP — Unshielded twisted pair 10BASE-T is the preferred Ethernet medium of the 90s. It is based on a star topology and provides a number of advantages over coaxial media.
It uses inexpensive, readily available copper phone wire. UTP wire is much easier to install and debug than coax. UTP uses RG-45 connectors, which are cheap and reliable.

What is a router? What is a gateway?
Routers are machines that direct a packet through the maze of networks that stand between its source and destination. Normally a router is used for internal networks while a gateway acts a door for the packet to reach the ‘outside’ of the internal network

What is Semaphore? What is deadlock?
Semaphore is a synchronization tool to solve critical-section problem, can be used to control access to the critical section for a process or thread. The main disadvantage (same of mutual-exclusion) is require busy waiting. It will create problems in a multiprogramming system, where a single CPU is shared among many processes.
Busy waiting wastes CPU cycles.
Deadlock is a situation when two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting processes. The implementation of a semaphore with a waiting queue may result in this situation.

Basic Networkin Questions - 2, 142

What does the Mount protocol do ?
The Mount protocol returns a file handle and the name of the file system in which a requested file resides. The message is sent to the client from the server after reception of a client's request.

What is anonymous FTP and why would you use it?
Anonymous FTP enables users to connect to a host without using a valid login and password. Usually, anonymous FTP uses a login called anonymous or guest, with the password usually requesting the user's ID for tracking purposes only. Anonymous FTP is used to enable a large number of users to access files on the host without having to go to the trouble of setting up logins for them all. Anonymous FTP systems usually have strict controls over the areas an anonymous user can access.

What is the Network Time Protocol?
The Network Time Protocol is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (Jitter).NTP is one of the oldest Internet protocols still in use (since before 1985).

What is a pseudo tty?
In Unix, a pseudo terminal is a pseudo-device pair that provides a text terminal interface without associated virtual console, computer terminal or serial port hardware. Instead, a process replaces the role of the underlying hardware for the pseudo terminal session.For each pseudo terminal, the operating system kernel provides two character devices: a master device and a slave device.The master and slave devices, in their most common deployment, form an association between a Unix shell and a terminal emulation program or some sort of network server.The slave device file, which generally has a nomenclature of /dev/ttyp*, has the appearance and supported system calls of any text terminal. Thus it has the understanding of a login session and session leader process (which is typically the shell program).The master device file, which generally has a nomenclature of /dev/ptyp*, is the endpoint for communication with the terminal emulator. It receives the control requests and information from the other party over this interface and responds accordingly.

What is External Data Representation?
eXternal Data Representation (XDR) is an IETF standard from 1995 of the presentation layer in the OSI model. XDR allows data to be wrapped in an architecture independent manner so data can be transferred between heterogeneous computer systems. Converting from the local representation to XDR is called encoding. Converting from XDR to the local representation is called decoding. XDR is implemented as a software library of functions that is portable between different operating systems and is also independent of the transport layer.

What is the difference between interior and exterior neighbor gateways?
Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside world.

What are 10Base2, 10Base5 and 10BaseT Ethernet LANs ?
10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with a contiguous cable segment length of 100
meters and a maximum of 2 segments.
10Base5—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with 5 continuous segments not exceeding 100
meters per segment.
10BaseT—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling and twisted pair cabling.

BOOTP helps a diskless workstation boot. How does it get a message to the network looking for its IP address and the location of its operating system boot files ?
BOOTP sends a UDP message with a subnetwork broadcast address and waits for a reply from a server that gives it the IP address. The same message might contain the name of the machine that has the boot files on it. If the boot image location is not specified, the workstation sends another UDP message to query the server

What protocol is used by DNS name servers ?
DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a connectionless protocol offers. Of course, transmission reliability suffers with UDP.

Which are the three types of routing tables ?
The three types of routing tables are fixed, dynamic, and fixed central. The fixed table must be manually modified every time there is a change. A dynamic table changes its information based on network traffic, reducing the amount of manual maintenance. A fixed central table lets a manager modify only one table, which is then read by other devices. The fixed central table reduces the need to update each machine's table, as with the fixed table. Usually a dynamic table causes the fewest problems for a network administrator, although the table's contents can change without the administrator being aware of the change.

Basic Networkin Questions - 1 140

What is source-route bridging algorithm ?
The source-route bridging (SRB) algorithm was developed by IBM and was proposed to the IEEE 802.5 committee as the means to bridge between all LANs. SRBs are so named because they assume that the complete source-to-destination route is placed in all inter-LAN frames sent by the source. SRBs store and forward the frames as indicated by the route appearing in the appropriate frame field. Assume that Host X wants to send a frame to Host Y. Initially, Host X does not know whether Host Y resides on the same LAN or a different LAN. To determine this, Host X sends out a test frame. If that frame returns to Host X without a positive indication that Host Y has seen it, Host X assumes that Host Y is on a remote segment. To determine the exact remote location of Host Y, Host X sends an explorer frame. Each bridge receiving the explorer frame copies the frame onto all outbound ports. Route information is added to the explorer frames as they travel through the internetwork. When Host X's explorer frames reach Host Y, Host Y replies to each individually, using the accumulated route information. Upon receipt of all response frames, Host X chooses a path based on some predetermined criteria. Host X must select one of these two routes. The IEEE 802.5 specification does not mandate the criteria that Host X should use in choosing a route, but it does make several suggestions, including the following:
•First frame received
•Response with the minimum number of hops
•Response with the largest allowed frame size
•Various combinations of the preceding criteria
In most cases, the path contained in the first frame received is used.


What is Transparent Bridge ?
Transparent bridges were first developed at Digital Equipment Corporation (Digital) in
the early 1980s. Transparent bridges are so named because their presence and operation are transparent to network hosts. When transparent bridges are powered on, they learn the workstation locations by analyzing the source address of incoming frames from all attached networks. For example, if a bridge sees a frame arrive on port 1 from Host A, the bridge concludes that Host A can be reached through the segment connected to port 1. Through this process, transparent bridges build a table. The bridge uses its table as the basis for traffic forwarding. When a frame is received on one of the bridge's interfaces, the bridge looks up the frame's destination address in its internal table. If the table contains an association between the destination address and any of the bridge's ports aside from the one on which the frame was received, the frame is forwarded out the indicated port. If no association is found, the frame is flooded to all ports except the inbound port. Broadcasts and multicasts also are flooded in this way. Transparent bridges successfully isolate intrasegment traffic, thereby reducing the traffic seen on each individual segment. This is called filtering and occurs when the source and destination MAC addresses reside on the same bridge interface. Filtering usually improves network response times, as seen by the user. The extent to which traffic is reduced and response times are improved depends on the volume of intersegment traffic relative to the total traffic, as well as the volume of broadcast and multicast traffic.


What is the basic difference between transparent bridges and source-route bridges relative to the forwarding processes ?
In a transparent bridged environment, bridges determine whether a frame needs to be forwarded, and through what path based upon local bridge tables. In an SRB network, the source device prescribes the route to the destination and indicates the desired path in the RIF.


What is Switched Multimegabit Data Service ?
Switched Multimegabit Data Service (SMDS) is a high-speed, packet-switched, datagram-based WAN networking technology used for communication over public data networks (PDNs). SMDS can use fiber- or copper-based media. SMDS networks consist of several underlying devices to provide high-speed data service. These include customer premises equipment (CPE), carrier equipment, and the subscriber network interface (SNI). CPE is terminal equipment typically owned and maintained by the customer. CPE includes end devices, such as terminals and personal computers, and intermediate nodes, such as routers, modems, and multiplexers. Intermediate nodes, however, sometimes are provided by the SMDS carrier. Carrier equipment generally consists of high-speed WAN switches that must conform to certain network equipment specifications. These specifications define network operations, the interface between a local carrier network and a long-distance carrier network, and the interface between two switches inside a single carrier network.


Where is SMDS Interface Protocol used ?
The SMDS Interface Protocol (SIP) is used for communications between CPE (Customer premises equipment) and SMDS (Switched Multimegabit Data Service) carrier equipment. SIP provides connectionless service across the subscriber network interface (SNI), allowing the CPE to access the SMDS network.

What is Data-Link Switching ?
Data-link switching (DLSw) provides a means of transporting IBM Systems Network Architecture (SNA) and network basic input/output system (NetBIOS) traffic over an IP network. It serves as an alternative to source-route bridging (SRB), a protocol for transporting SNA and NetBIOS traffic in Token Ring environments that was widely deployed before the introduction of DLSw. In general, DLSw addresses some of the shortcomings of SRB for certain communication requirements—particularly in WAN implementations. This chapter contrasts DLSw with SRB, summarizes underlying protocols, and provides a synopsis of normal protocol operations. The three primary functions of DLSw are :
•The Switch-to-Switch Protocol (SSP) is the protocol maintained between two DLSw nodes or routers.
•The termination of SNA data-link control (DLC) connections helps to reduce the likelihood of link layer timeouts across WANs.
•The local mapping of DLC connections to a DLSw circuit.

What is Banyan VINES ?
Banyan Virtual Integrated Network Service (VINES) implements a distributed network operating system based on a proprietary protocol family derived from the Xerox Corporation's Xerox Network Systems (XNS) protocols. VINES uses a client/server architecture in which clients request certain services, such as file and printer access, from servers.

What is Enhanced Interior Gateway Routing Protocol ?
The Enhanced Interior Gateway Routing Protocol (EIGRP) represents an evolution from its predecessor IGRP. This evolution resulted from changes in networking and the demands of diverse, large-scale internetworks. EIGRP integrates the capabilities of link-state protocols into distance vector protocols. Additionally, EIGRP contains several important protocols that greatly increase its operational efficiency relative to other routing protocols. One of these protocols is the Diffusing update algorithm (DUAL). DUAL enables EIGRP routers to determine whether a path advertised by a neighbor is looped or loop-free, and allows a router running EIGRP to find alternate paths without waiting on updates from other routers. EIGRP provides compatibility and seamless interoperation with IGRP routers. An automatic-redistribution mechanism allows IGRP routes to be imported into EIGRP, and vice versa, so it is possible to add EIGRP gradually into an existing IGRP network. Because the metrics for both protocols are directly translatable, they are as easily comparable as if they were routes that originated in their own autonomous systems (ASs). In addition, EIGRP treats IGRP routes as external routes and provides a way for the network administrator to customize them.

Name the four key technologies that are used by EIGRP ?
EIGRP employs four key technologies, including neighbor discover/recovery, Reliable Transport Protocol (RTP), Diffusing Update ALgorithm (DUAL) finite-state machine, and a modular architecture that enables support for new protocols to be easily added to an existing network.

Why EIGRP is more efficient in operation than IGRP ?
Unlike most other distance vector routing protocols, EIGRP does not mandate a periodic update of routing tables between neighboring routers. Instead, it employs a neighbor discovery/recovery mechanism to ensure that neighbors remain aware of each other's accessibility. As long as a router receives periodic hello packets from its neighbors, it can assume that those neighbors remain functional. More importantly, it can assume that all of its routes that rely upon passage through those neighbors remain usable. Thus, EIGRP is much more efficient than conventional distance vector routing protocols because it imposes much less overhead on routers and transmission facilities during normal operation.

What is Interior Gateway Protocol ?
IGRP is a distance vector Interior Gateway Protocol (IGP). Distance vector routing protocols mathematically compare routes using some measurement of distance. This measurement is known as the distance vector. Routers using a distance vector protocol must send all or a portion of their routing table in a routing-update message at regular intervals to each of their neighboring routers. As routing information proliferates through the network, routers can identify new destinations as they are added to the network, learn of failures in the network, and, most importantly, calculate distances to all known destinations.

Networking, Socket Programming, Inter-Process Communication... 138

• How do I monitor the activity of sockets?
• How would I put my socket in non-blocking mode?
• What are RAW sockets?
• What is the role of TCP protocol and IP protocol.
• What is UDP?
• How can I make my server a daemon?
• How should I choose a port number for my server?
• Layers in TCP/IP
• How can I be sure that a UDP message is received?
• How to get IP header of a UDP message
• Writing UDP/SOCK_DGRAM applications
• How many bytes in an IPX network address?
• What is the difference between MUTEX and Semaphore?
• What is priority inversion?
• Different Solutions to dining philosophers problem.
• What is a message queue?
• Questions on Shared Memory.
• What is DHCP?
• Working of ping, telnet, gopher.
• Can I connect two computers to internet using same line ?
• Working of TCP and SSL Handshake
• How P2P softwares work?
• Setting up TOMCAT web service
• Port numbers for FTP, HTTP, telnet, POP, finger
• Difference - Passive FTP, Active FTP
• Maximum Transmission Unit (MTU) what is it?
• Security threats due to use of CGI
• What is "spoofing"
• Where could you find Apache server web log
• Find web visitors by country
• What is Virtual Private Network (VPN) and how does it work?
• How does routing work?
• User(s) are complaining of delays when using the network. What would you do?
• What are some of the problems associated with operating a switched LAN?
• Name some of the ways of combining TCP/IP traffic and SNA traffic over the same link.
• What sort of cabling is suitable for Fast Ethernet protocols?
• What is a Class D IP address?
• Why do I sometimes lose a server's address when using more than one server?

Networking Interview questions 134

Computer Networking Interview Questions

Here are the basic interview questions for the network administrators, system administrators and IT manager posts. These questions provide the basic information about the network communication technology, network topologies, network troubleshooting techniques, network devices and the basic overview of the LAN/WAN communication model.

What is DHCP?

DHCP stands for Dynamic Host Configuration Technology. The basic purpose of the DHCP is to assign the IP addresses and the other network configuration such as DNS, Gateway and other network settings to the client computers. DHCP reduces the administrative task of manually assigning the IP addresses to the large number of the computers in a network.

What is DNS and how it works?

DNS stands for Domain name system and it translates (converts) the host name into the IP address and IP address into to the host name. Every domain and the computer on the internet is assigned a unique IP address. The communication on the internet and in the network is based on the IP addresses. IP addresses are in this format 10.1.1.100, 220.12.1.22.3, 1.1.1.1 etc. IP addresses can’t be remembered but the host names (e.g. www.networktutorials.info, xyz.com, abc.com) are easy to remember instead of their IP addresses.

What is a Firewall?

Firewall is a protective boundary for a network and it prevents the unauthorized access to a network. Most of the Windows operating system such as Windows XP Professional has built-in firewall utilities. There are the large number of the third party firewall software and the basic purpose of all the firewall software and hardware is same i.e. to block the unauthorized user access to a network.

What is WAN?

WAN stands for wide area network and it covers the broader geographical area. Basically there are three types of a computer network LAN (Local Area Network), MAN (Metropolitan Area Network) and WAN (Wide Area Network). The communication in a WAN is based on the Routers. A WAN network can cover a city, country or continents.

Define VOIP Communication Technology

VOIP stands for Voice over IP and this technology is used for transmitted the voice over the IP based long distance network to make phone calls. VOIP phone calls are very cheap and a large number of the corporate offices and home users are using VOIP technology to make long distance phone calls.

What is Wi Max Technology?

Wi Max is a wireless broadband technology and it is a advance shape of the Wi Fi (which was a base band technology). Wi Max supports data, video and audio communication at the same time at a very high speed up to 70 Mbps.

Define Network Gateway

Network Gateway can be software or a hardware. A gateway is usually a joining point in a network i.e. it connects two networks. A computer with two LAN cards can act as a gateway.

What is a Router?

A router routes the traffic to its destination based on the source and destination IP addresses, which are placed in the routing software known as routing table.

How Fiber Optic Cable Works

Fiber optics provides the fastest communication medium for data and voice. Data can travel at the speed of light through the fiber optic cables. ISPs and corporate offices are usually connected with each other with the fiber optic cables to provide high speed connectivity.

What is File Server?

A file server is a computer in a network that authenticates the user access in a network such as Windows 2000/2003 Servers.

Define Seven Layers of OSI Model

There are seven layers of the OSI model. The basic purpose of these layers is to understand the communication system and data transmission steps. The seven layers are Application, Presentation, Session, Transport, Network, Data Link and Physical. You can remember the name of these layers by this phrase. “All people seems to need data processing”.

Define GSM Technology

GSM is a short range wireless technology and is usually used in the mobile phones, hand help devices, MP3 players, Laptops, computers and in cars.

B. Bashir manages this website Networking Tutorials and regularly writes articles on various topics such as Computer Networking, www.networktutorials.info/communication_types.html" title="Networking Tutorials">Network Communication Technology Wireless Networking, Computer Hardware, Certifications, How Tos.

Networking Interview questions 130

Learn the basic interview questions for the network administrator, system administrator and IT manager jobs. You will get an basic overview of LAN, WAN, Router, Gateway, Wi Max technology, DNS, DHCP, Fiber optic, GSM and voip communication technology.


Computer Networking Interview Questions

Here are the basic interview questions for the network administrators, system administrators and IT manager posts. These questions provide the basic information about the network communication technology, network topologies, network troubleshooting techniques, network devices and the basic overview of the LAN/WAN communication model.

What is DHCP?

DHCP stands for Dynamic Host Configuration Technology. The basic purpose of the DHCP is to assign the IP addresses and the other network configuration such as DNS, Gateway and other network settings to the client computers. DHCP reduces the administrative task of manually assigning the IP addresses to the large number of the computers in a network.

What is DNS and how it works?

DNS stands for Domain name system and it translates (converts) the host name into the IP address and IP address into to the host name. Every domain and the computer on the internet is assigned a unique IP address. The communication on the internet and in the network is based on the IP addresses. IP addresses are in this format 10.1.1.100, 220.12.1.22.3, 1.1.1.1 etc. IP addresses can’t be remembered but the host names (e.g. www.networktutorials.info, xyz.com, abc.com) are easy to remember instead of their IP addresses.

What is a Firewall?

Firewall is a protective boundary for a network and it prevents the unauthorized access to a network. Most of the Windows operating system such as Windows XP Professional has built-in firewall utilities. There are the large number of the third party firewall software and the basic purpose of all the firewall software and hardware is same i.e. to block the unauthorized user access to a network.

What is WAN?

WAN stands for wide area network and it covers the broader geographical area. Basically there are three types of a computer network LAN (Local Area Network), MAN (Metropolitan Area Network) and WAN (Wide Area Network). The communication in a WAN is based on the Routers. A WAN network can cover a city, country or continents.

Define VOIP Communication Technology

VOIP stands for Voice over IP and this technology is used for transmitted the voice over the IP based long distance network to make phone calls. VOIP phone calls are very cheap and a large number of the corporate offices and home users are using VOIP technology to make long distance phone calls.

What is Wi Max Technology?

Wi Max is a wireless broadband technology and it is a advance shape of the Wi Fi (which was a base band technology). Wi Max supports data, video and audio communication at the same time at a very high speed up to 70 Mbps.

Define Network Gateway

Network Gateway can be software or a hardware. A gateway is usually a joining point in a network i.e. it connects two networks. A computer with two LAN cards can act as a gateway.

What is a Router?

A router routes the traffic to its destination based on the source and destination IP addresses, which are placed in the routing software known as routing table.

How Fiber Optic Cable Works

Fiber optics provides the fastest communication medium for data and voice. Data can travel at the speed of light through the fiber optic cables. ISPs and corporate offices are usually connected with each other with the fiber optic cables to provide high speed connectivity.

What is File Server?

A file server is a computer in a network that authenticates the user access in a network such as Windows 2000/2003 Servers.

Define Seven Layers of OSI Model

There are seven layers of the OSI model. The basic purpose of these layers is to understand the communication system and data transmission steps. The seven layers are Application, Presentation, Session, Transport, Network, Data Link and Physical. You can remember the name of these layers by this phrase. “All people seems to need data processing”.

Define GSM Technology

GSM is a short range wireless technology and is usually used in the mobile phones, hand help devices, MP3 players, Laptops, computers and in cars.

About Author

B. Bashir manages this website Networking Tutorials and regularly writes articles on various topics such as Computer Networking, Designing a Network Server Wireless Networking, Computer Hardware, Certifications, How Tos, Optical Network Tutorial and computer tips.

Computer Networking Interview Questions 128

10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with a contiguous cable segment length of 100
meters and a maximum of 2 segments.
10Base5—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling, with 5 continuous segments not exceeding 100
meters per segment.
10BaseT—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband
signaling and twisted pair cabling.
4. Explain a Management Information Base (MIB)
A Management Information Base is part of every SNMP-managed device. Each SNMP agent has the MIB database that
contains information about the device's status, its
performance, connections, and configuration. The MIB is queried by SNMP.
5. Explain anonymous FTP and why would you use it
Anonymous FTP enables users to connect to a host without using a valid login and password. Usually, anonymous FTP
uses a login called anonymous or guest, with the
password usually requesting the user's ID for tracking purposes only. Anonymous FTP is used to enable a large number
of users to aCNess files on the host without having
to go to the trouble of setting up logins for them all. Anonymous FTP systems usually have strict controls over the areas
an anonymous user can aCNess.

Networking Interview Questions 126

Basics
· Can you define protocol?
· Can you explain the concept of OSI layer?
· Can you explain the different layers in OSI model?
· Can you explain Application layer in OSI model?
· Can you explain Presentation layer in OSI model?
· Is it compulsory that compression, encryption and translation functions will be
used during communication?
· Can you explain Session layer in OSI model?
· What’s the concept of Simplex, Half Duplex and Full Duplex dialogs?
· What are the different types of dialogs in Session layer?
· Can you explain Transport layer in OSI model?
· Can you explain the concept of Congestion?
· Can you explain Network Layer?
· Can you explain Data link Layer?
· Can you explain the Physical layer?
· Can you explain what an IP address is?
· How to convert Decimal to Binary?
· How many IP addresses can come in IPV4?
· Can you explain the concept of Unicast IP address?
· Can you explain the concept of IP multicasting or multicast IP address?
· How many different types of subnet classful networks are present?
· What are the IP address ranges for public and private IP address?
· Why do we need class and how many different types of class exists?
· How are the IP addresses distributed between different classes?
· Can you explain what is classful IP addressing?
· Can you explain the concept of subnetting?
· What are the advantages of using subneting?
· If the host has the subnet ID why do we need a subnet mask?
· How is network address calculated from the subnet?
· What is the advantage of using classless addressing over classful addressing
scheme?
· Can you explain the concept of CIDR?
· Twist: - Can you explain superneting?
· Can you explain concept of custom subneting?
· What is the implication of increasing and decreasing subnet Bits?
· Why do we need to subtract two from number of hosts?
· Can you explain the concept of VLSM?
· Can you explain IP packet in detail?

Routers
· Can you explain the concept of DPU, Segments, Datagram, Frame and packet?
· What is IP datagram fragmentation and MTU?
· Can you explain in detail with example how data fragmentation works?
· Larger the IP datagram less the overhead, is it true or false?
· What is the minimum size of MTU bytes?
· Can you explain how optimal MTU size is calculated?
· How does the IP message finally reassemble?
· Can you explain the concept of Repeaters, Hubs, Bridges, Switches and Routers?
· On what layers do router, switches, bridges and hubs operate?
· Can you explain the concept of Layer 3 switches?
· What are CSU, DSU and TSU?
· What are the basic components of the router?
· Can you explain the WAN and LAN Interface in Routers?
· What are DB-15, DB-60 and RJ-45 in CISCO routers?
· Can you explain the concept of TTL?
· What is the concept of ICMP packets?
· Which operating system does CISCO have?
· Can you explain the concept of NAT?
· How is NAT implemented?
· Can you explain how actually NAT works?
· Why does collision occur in HUBS and repeaters?
· Can you explain the concept of Collision domain?
· What is the concept of routing tables?
· What is the use of route print?
· Can you explain how in detail how routing table looks like?
· How can you see route tables on the router?
· Can you explain the concept of static and dynamic routing?
· When to use Static routes and dynamic routes?
· How do you configure static routes on a router?
· Can you explain static default routes?
· What is the advantage of using Static default routes?
· Why do workstations have route tables?
· What is the concept of gateway of last resort?
· Can you explain the concept of routing protocol?
· What activities does routing protocol perform?
· What metrics are used by routing protocols to determine the best path?
· Can you explain what is interior and exterior routing protocols?
· Can you explain the concept of intradomain and interdomain routing protocols?
· Can you explain the concept of internet work and intranet work routing protocols?
· Which method does routing protocol use to determine shortest path?
· What is distance vector routing protocol?
· How do routers share information in Distance Vector routing?
· What is the main issue with routing by rumor?
· Can you explain the count-to- infinity problem in distance vector?
· How is metric or the cost calculated for Distance Vector routing protocol?
· What is the main issue with hop count metric issue?
· Can you explain how Link-State routing protocols work?
· Can you explain the concept of broad cast and multi-cast?
· Can you tell which protocols falls in Distance vector and which in Link-State?
· What’s the difference between distance vector and link-state protocol?
· Can you explain difference between Single path and Multipath?
· Can you explain route summarization?
· How are the series of IP combined in to one route path in route summarization?
· Can you explain RIP protocol?
· How is route table populated by RIP protocol?
· Can you explain convergence in networks?
· Can you explain RIP timers in detail?
· Can you explain routing loop issue in RIP protocol?
· How do we avoid routing loop issue in RIP?
· In RIP why do we have HOP count of 15?
· How do we disable auto-summarization in RIP?
· Can you explain IGRP?
· How does IGRP work?
· How many timers does IGRP have?
· How does IGRP calculate metric?
· Can multiple instance of IGRP run on one physical router?
· How is load balancing done in IGRP?
· What’s the command to configure IGRP?
· Can you explain EIGRP?
· What does neighbor terminology mean in EIGRP?
· What are different types of packets in EIGRP?
· How does EIGRP protocol update route information to its neighbors?
· What is the concept of successor in EIGRP?
· What is DUAL in EIGRP?
· Can you explain reported distance (RD), feasibility distance (FD) and Feasibility
condition (FC)?
· Can you explain the concept of successor and feasible successor?
· Can you explain passive and active route states?
· What is SIA or stuck in active?
· How do packets and timers in EIGRP work?
· What are the different tables used in EIGRP?
· Can you explain EIGRP metrics?
· Can you explain how EIGRP finds its successor and feasible successor?
· Can you explain Active and Passive route?
· Can you explain OSPF?
· How does OSPF populate route table?
· What are the different tables in OSPF?
· Can you explain different areas in OSPF?
· Can you explain different router types in OSPF?
· Can you explain Designated Router and Backup designated router?
· Can you explain different router states in OSPF?
· Can you explain different OSPF packet types?
· What are the different types of OSPF timers?
· How SPF algorithm does the route determination?
· Can you explain autonomous system?
· What are different types of dynamic protocols?
· Can you explain autonomous numbers in EGP?
· What is BGP?
· What is the concept of BGP speakers and Peers?
· What is EBGP and IBGP?
· What is RIB?
· Can you explain the concept of BGP confederations?
· What are BGP path attributes?
· What is the concept of NLRI?
· How are routing neighbors discovered in BGP?
· Can you explain how BGP does the decision process?
· What is the concept of redistribution?
· Can you explain the concept of one way redistribution and mutual distribution?
· How does metric translation takes place in redistributing routes?

Firewall
· Can you define what a FIREWALL is?
· What are the different types of firewalls?
· Can you explain packet filtering firewall?
· Can you explain circuit level gateway?
· Can you explain stateful inspection?
· What is Application Gateway?
· Is NAT a firewall?
· Are personal firewall actually firewalls?
· Can you explain the concept of demilitarized zone?
· What is the meaning of bastion host?
· What are the different types of firewall architectures?
· Can you explain dual home architecture?
· Can you explain screened host architecture?
· Can you explain screened subnet architecture?
· What is the use of perimeter area?
· What is IP spoofing and how can it be prevented?
· Which firewall have you worked with?

VPN
· Can you explain the difference between trusted and untrusted networks?
· Can you define in short what VPN is?
· What are the different types of VPN?
· What requirements should a VPN fulfill?
· How many ways are there to implement VPN architecture?
· What are the different ways authentication mechanism in VPN?
· Can you explain the basic of encryption in VPN?
· What’s the difference between Symmetric and Asymmetric cryptosystem?
· What are the different symmetric algorithms?
· What are the disadvantages of symmetric algorithms?
· What are the different asymmetric algorithms?
· Can you explain different components in PKI?
· What is a digital certificate?
· Can you explain tunneling?
· What is the concept of HA and FA in VPN tunneling?
· Can you explain VPN tunneled packet in detail?
· Can you explain voluntary and compulsory tunnels?
· Can you explain static and dynamic tunnels?
· Can you explain encapsulating, carrier and passenger protocol?
· On which layer does L2F, PPTP and L2TP operate?
· Can you explain PPP protocol?
· Can you explain PPP link process step by step?
· Can you explain PPP packet format?
· How does PPP use LCP for link control?
· Can you explain PPTP (Point-to-Point Tunneling Protocol)?
· What is GRE in PPTP?
· How does PPTP encapsulate data?
· Can you explain CHAP?
· Can you explain PAP?
· What does PPTP use for encryption and authentication?
· What is a L2F protocol?
· Can you explain the broader steps of how L2F establishes the tunnel?
· Can you explain how L2F data tunneling process works?
· How do we do encryption and authentication in L2F?
· Can you explain L2TP?
· Can you define LAC and LNS?
· How does L2TP process?
· How do we do encryption and authentication in L2TP?
· Can you explain what IPSec is?
· Can you give an overview of various components in IPSec?
· In IPSec what is SAD, SPD and SA’s?
· Can you explain in a generic manner the packet of IPSec?
· Can you describe the Authentication Header (AH) Protocol?
· What is ESP (Encapsulating Security Payload)?
· What is Transport and Tunnel mode?
· Can you explain IKE (Internet Key Exchange)?
· Can you explain IKE phases?
· Can you explain IKE modes?
· Can you explain transport and tunnel mode in detail with datagram packets?

Protocols and other questions
· What is NetBIOS protocol?
· Can you explain what the use of IGMP Protocol is?
· What are the different types of host in multicasting?
· Can you explain Ping and Tracert?
· How do you continuously ping an IP Address?
· How does Tracert actually work?
· What is the use of RTP and RTCP Protocol?
· Can you explain RTP in Detail?
· Can you explain RTP multiplexing in detail?
· Can you explain format of RTP and RTCP packets?
· Can you explain RSVP?
· Can you explain in detail how RSVP actually works?
· Can you explain RPC (Remote Procedure Calls)?
· Can you explain the RPC and Client server Architecture?
· Can you explain TCP IP Protocol?
· Can you explain the architecture of TCP IP Protocol?
· Can you explain TCP header in detail?
· Can you explain IP protocol?
· Can you explain the concept of CDMA?
· Can you explain the concept of DHCP?
· How does DHCP work?
· How can we configure DHCP?
· What is DNS?
· How do we control USB through a network?
· What is the difference between Windows 2000 and Windows 2003?
· What is a difference between a domain and workgroup?