Networking interview questions

IP addressing: It is 32 bit logical binary number with 4 octets each octane containing 8 bits separated by dotted decimal.

Subnet-mask: it distinguishes the network and host portion

Default gateway: it is an entry and exit point of a network.

IANA(Internet Assigned Numbers Authority) is the body which gives the IP addresses. IANA is divided into 3 (RIR’s)
Regional Internet Registries are corporations established for the purpose of administration and registration of IP address
and autonomous system numbers.

Internic: internet work information centre
Arnica: American registry network information centre
Apnic: Asia pacific network information centre.

IP addresses are of 2 types:

Public IP address:
IP addresses which we have to buy from ISP’s and are registered IP addresses
Private IP address:
IP addresses which we can use in our own organization & we don’t need to buy these addresses.

IP add are divided into different classes

Class range usage host capacity private range
A 1-126 Host 16 Million 10.0.0.0 – 10.255.255.255
B 128-191 Host 65535 172.16.0.0 –172.31.255.255
C 192-223 Host 254 192.168.0.0-192.168.255.255
D 224-239 Multicasting -- --
E 240-254 Reserved for future -- --

OSI Layers

The international standard for organization has developed the OSI reference model to describe how the data is
transferred from one machine to another, from the point where the user starts entering the information using mouse &
keyboard to when that information Is converted to electrical or light signals transferred along a piece of wire or radio
waves transferred through the air.
The OSI reference model describes concepts and terms nicely into the scheme explained in OSI model. The OSI scheme is
only theory to study. ISO developed the seven layer model to help vendors & n/w administrators to gain a better
understanding of how data is handled and transported between networking devices.

There are 7 layers in the OSI reference model,

APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
DATALINK
PHYSICAL

The first 3 layers are part of the user’s application the remaining 4 layers are responsible for moving the information
back and forth between these high layers. Each layer is responsible for a specific process or role

OSI LAYERS

OSI: Stands for Open System Interconnection there are total seven layers it is only theory for study it studies how the
data is transferred from one place to another. OSI is standard network architecture.

7 APPLICATION

6 PRESENTATION

5 SESSION

4 TRANSPORT

3 NETWORK

2 DATA LINK

1 PHYSICAL

Application:-this layer gives interface to the end user or browser. Application layer gives flexibility to execute some talks
[application protocols are www, ftp, telnet, http, smtp, etc]

Presentation:- is responsible for representing the data. It converts ASCII, adbc, jpeg, midi, gif etc. into binary *0’s and
1’s+ and send and again from binary it converts into ascii, adbc etc *audio, vdo, image files+ and displays on the users
screen. This layer converts, represents compresses, encrypts decrypts and hides etc

Session: - it defines how to start, control and end session i.e it establishes the session, it manages and terminates.
Protocols for session layer are net bios nfs, nis, rpc etc. this layer checks whether the destination host is alive or not. It
manages and terminates the task. If the destination is alive or not it manages send the data and then terminates the
task. First it checks whether the destination host is alive or not if alive then sends and terminates if dead then gives the
message that the destination host is dead or offline.

Transport layer:

This layer segments data to be passed down to the network layer and reassembles for the
Session and Upper layers.
It provides the flow control to overcome congestion in the receiving host’s buffer’s.
It provides the choice of TCP and UDP

Basic difference between TCP and UDP

TCP
1. It is connection oriented reliable but slow
2. It is used for data transmission
3. Eg: it is like a Volvo bus [luxury] it takes passengers [data] very comfortably and on whom passengers can rely, so
that they reach their destination safely. There is no data loss and if the message or data is not send then it gives the
confirmation that the data is sent or not.
UDP
1. It is connection less, no reliability Very fast.
2. It is used for voice transmission
3. Eg: it is like RTC bus [ordinary] it takes passengers very roughly without caring about the passengers, passengers
cannot rely on, because there will be no guarantee that the passengers will reach their destination safely, there will
be data loss in this and there is no confirmation if the data is sent or not.

Network layer: [routing]
Defines the Network Address
Router Operates this Layer
Segments from Transport Layer are placed into Packet and passed down to the Network Layer.
Network Layer maintains Routing Table.
It is responsible for forwarding the packets using the best shortest path (nic converts the data).

Data link:-[frame]
Packets from the network Layer are Placed into Frames
Data Link Layer handles physical transmission of data from one node to another.
IEEE subdivided this Layer into 2 sublayers:
Logical Link Control(LLC):
It uses Destination Service Access Point(DSAP) and Source Services Access Point(SSAP)
Media Access Control(MAC):
Builds Frames from Bits
It is our nic card; it will attach the Mac address and create a frame so that the data reaches to the desired destination.
Nic will transfer it to physical cable.

Flow Control
Another communications control defined on the LLC sublayer is flow control. The Transport layer of the OSI model
actually manages the mechanisms used to control the flow of data between two hosts. The Data Link layer defines the
data values used in the flow control signaling between two transmitting hosts.
There are two types of flow control implemented in data communications - software and hardware:
Software flow control, common to networking, involves a process called XON/XOFF, whih roughly stands for
transmission on/transmission off.
Hardware flow control, also called RTS/CTS (ready to send/clear to send), uses two wires in a cable, one for RTS and one
for CTS. When either is turned off, the flow is interrupted

LLC is logical link control.
LLC functions are:
.error control
.flow control

Data encapsulation by OSI Layer:
OSI Layer Encapsulation
Transport Segment
Network Packet
Data Link Frame
Physical Bits

Physical layer:- means physical cable it converts the data into binary

DATA DATA GRAM PACKETS FRAMES BITS

1. The 1 layer of tcp/ip “application” works the same work done by the 3 layers of OSI “application, presentation &
session”.
2. The layer of tcp/ip “host to host” does the same work done by the layer of OSI “transport”.
3. The layer of tcp/ip “ip layer” does the same work done by the layer of OSI ”network”.
4. The layer of tcp/ip “network” does the same work done by the 2 layer of OSI “data link physical”.

CISCO Introduction

Few well known protocol numbers:

Port numbers Host-to-Host Layer Protocol
1 Internet Control Message Protocol (ICMP)
2 Internet Group Management Protocol (IGMP)
3 Gateway to Gateway Protocol (GGP)
4 IP in IP
6 Transmission Control Protocol (TCP)
8 Exterior Gateway Protocol (EGP)
17 User Datagram Protocol (UDP)
35 Inter-Domain Policy Routing Protocol (IDPR)
45 Inter-Domain Routing Protocol (IDRP)
46 Resource Reservation Protocol (RSVP)
47 Generic Routing Encapsulation (GRE)
54 NBMA Next Hop Resolution Protoco (NHRP)
88 Cisco Internet Gateway Routing Protocol (IGRP)
89 Open Shortest Path First (OSPF)

isco routers and switches.
700, 800, 1600, 1700, 2500, 2600, 3600, 6000, 7000, 10000, 12000

700-2500 fixed routers
2600-12000 modular and multilayer

External layout of a Cisco 2500 series router

External layout of a Fixed Router

2500 Router—rear view

PROCESSOR

RA M POWER SWITCH
NV RAM

FLASH

ROM POWER SOCKET

EXHAUST FAN

F N
R L V R
A A R O
M S A M
H M

ROM – POST, BOOT UP, MINI IOS, BIOS
FLASH – IOS, SEARCHES FOR THE IOS AND THEN LOADS IT.
NVRAM – ANY SAVED CONFIG, START-UP CONFIG, USER MODE
RAM – TEMPORARY MEMORY, SET UP MODE

Accessing your router using HyperTerminal

Hyper terminal is terminal emulation software with which you can see the routers desktop without any ip add. This
software comes with every operating system in
Windows – hyper terminal
Unix – Kermit (kernel is the internal architecture)
Linux - minicom

Double click on HyperTerminal the window appears provide a name for the connection then if u want to change the icon
select the icon below. Then press enter then it will ask u for the port on which your console cable is connected select the
port. Then press enter the next window appears for the port setting for which u selected the port (com 1 or com 2) there
select restore defaults. After that u will see the console window then switch on the router.
USER MODE IS ALSO CALLED AS TROUBLE SHOOTING OR MONITORING MODE
ALL USER LEVEL COMMANDS WORK HERE

SHOW VER
SHOW FLASH
SHOW HISTORY
SHOW TERMINAL
TERMINAL HISTORY SIZE 50
SHOW CLOCK
SHOW USERS
SHOW HOSTS
SHOW RUNNING-CONFIG
SHOW STARTUP-CONFIG
COPY RUNNING-CONFIG STARTUP-CONFIG OR WRITE
ERASE STARTUP-CONFIG
CLOCK SET 10:00:00 01 MARCH 2007

GLOBAL CONFIGURATION MODE

WHATEVER YOU CONFIGURE HERE WILL BE GLOBAL TO THE ROUTER. U CAN ENTER THE GLOBAL PARAMETERS HERE
LIKE ASSIGNING A HOSTNAME, PASSWORDS ETC

HOSTNAME NETMETRIC
USERNAME AA PASSWORD 11
ENABLE PASSWORD CCNA
ENABLE SECRET CCNP

INTERFACE MODE

IN THIS MODE U CAN ASSIGN AN IP ADDRESS, NO SHUTDOWN ETC

INTERFACE SER 0, SER 1, ETHERNET 0
IP ADDRESS 10.1.1.1 255.0.0.0
NO SHUTDOWN

LINE MODE

U CAN CONFIGURE UR ROUTER BY 3 WAYS

CONSOLE CONFIGURING DIRECTLY FROM THE SYSTEM
AUXILIARY CONFIGURING THROUGH DIALUP CONNECTION REMOTELY
VTY 0 4 CONFIGURE THROUGH TELNET

Wide area network
LAN connections are within a company and WAN connections allow you to connect to remote sites. Wan connections
are very expensive and also it is slow comparatively to Ur LAN. We don’t own the infrastructure for WAN connections.
They are different companies who provide the wan connections like Telco. There are many services available for wan but
every service will be not available in the area where you want that service so before going for a wan connection u should
consider 2 things

Your connection requirement
Your cost of the solution

The first thing comes that can Ur company afford the expenditure that u will be selecting as solution for wan

We have multiple options to select for wan connection

Communication methods:-- wan protocols
Leased lines Hdlc
Isdn/Pstn Ppp or slip
X DSL / broadband frame-relay
Vsat Atm
Radio/ Wireless x.25

Wan connections fall under 4 categories :

Leased lines, these connections are referred to as point to point connection or dedicated connections it simulates a
single cable connection between the local and remote site.
Leased lines are pre-established wan communication path from dte to dce switch and again from dce switch to remote’s
dte for communication without any setup before sending data.
Lease lines use physical circuits.
It uses single synchronous serial lines up to 45 mbps [t3].
Leased lines are very expensive
Best suited when both of these conditions hold
The distance between the 2 sites is less, making them cost effective
You have a constant amount of traffic between 2 sites and need to guarantee bandwidth for certain application

Circuit switching
1. The term circuit switching means a phone call.
2. The advantage is cost u pay only the time u actually use.
3. No data can transfer before the end to end connection is established.
4. Circuit switch technology uses dialup modems or isdn connections,
5. It is used for low bandwidth data transfers.
6. Each time u dial it creates a physical circuit

Pstn[Public switched telephone network] Isdn [Integrated services digital network]
1. Analog signals 1. Digital signals
2. Slow speed 28.8 kbps 2. Speed up to 128 kbps
3. Either voice or data 3. Voice and data at a time simultaneously

Packet switching
1. Packet switched connections use logical circuits to make connection between two sites.
2. These logical circuits are referred to as virtual circuits *VC’s+ a logical circuit is built across any built physical
circuit.
3. In packet switch using one interface u can connect multiple interfaces,
4. In packet switching technology is used by frame-relay and Atm.

X DSL: (digital subscriber line) here x means it may be either A, B or C i.e. X, it is dedicated, cheaper, fast, telephone and
internet can be used at a time simultaneously

Broadband: Same functions like Xdsl but here internet and telephone can’t be used simultaneously only one at a time.
First broadband came then it turned into X-DSL

DCE: A DCE terminates a connection between two sites and provides clocking and synchronization for that connection.
By default Ur ISP’s device *switch+ is dce.

End point of WAN provider’s side of the communication facility. This is the point where responsibility changes from
service provider to customer.

DTE: data terminal equipment a dte may be our router or a pc it Terminates the Connection. By default the router is dte.

WAN PROTOCOLS

PPP HDLC
1. Point to point protocol 1. High level data link control protocol
2. Open standard 2. Cisco proprietary
3. Supports multilink 3. Doesn’t support multilink
4. Supports authentication 4. Doesn’t support authentication
5. Supports error correction and detection 5. Supports error detection
6. needs to configure 6. --
7. Supports compression 7. No Supports compression

LEASE LINE
SERVICE PROVIDER

V.35 G.703 G.703 V.35
AAA TELCO B

PAP CHAP

Works based on usernames Works based on hostnames
Less secure More secure
2way hand shake 3 way hand shake
When debugging is on msgs seen Are request When debugging is on msgs seen are
and acknowledgement challenge, Response and success.
p.w are sent in clear text p/w are sent in encrypted form md5 (mesge
digest5)
Performs authentication at 1 time. performs auth periodically

ATM Asynchronus Transfer Mode

Frame-relay is from ccna – ccie

If we see from technical point of view communication methods are:--

1. Broadcast multi access -------------------- ETHERNET
2. Point-to-point --------------------- HDLC, PPP, SLIP
3. Non broadcast multi access (NBMA)------- FRAME-RELAY (there is no broadcast capability)

Addresses can be

1. Unicast one-to-one
2. Multicast one-to-some/few
3. Broadcast one-to-all

Frame Relay Overview
DCE or
Frame
Relay
CSU/DS Switch
U

Frame Relay works
if one want to send thehere. only to a not to b and c that is nbma
message
using a single interface one can connect to multiple sites by creating multiple sub-

Interfaces on central office
Accesses multiple sites without capability of broadcast

1. It is the fastest wan protocol used to carry voice, vdo, data simultaneously with high
Speed. [64 kbps to 45 mbps (T3)]
2. using frame-relay bandwitdth can be committed called as cir and also the information is is guaranteed
3. Every frame-relay connection is identified by a number called dlci (data link connection
identifier) no.
4. Inverse ARP is the protocol which map local dlci to the destination ip (automatically it
does the mapping dynamically).
5. Frame-relay is secure because of tunnel topology.
6. Frame-relay supports traffic shaping.
7. Suitable for long distances because call to charminar and call to usa is same in frame-relay.

There are 2 types of encapsulation methods

Cisco (default) [meant for cisco routers only]
Ietf (internet engineering task force) (open standard) [meant for cisco and non-cisco
routers]

while configuring both the sides same encapsulation should be there
command: frame-relay lmi type cisco or ietf

frame-relay connection can be
point-to-point
point-to-multipoint
nbma
When mapping is done it will create a circuit between 2 routers. We call it as pvc. Virtual circuit because it is not a
physical connection. So until and unless the connection breaks between 2 routers the circuit is permanent. For each
connection one circuit is there.

LMI is the protocol which sends keepalive messages from frame-relay dte to dce, if ios is 11.0 and above the lmi is auto
detected.

There are three types of lmi

Cisco
q.933a
ansi

Networking interview questions

Networking interview questions

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