IP ROUTING - INTERVIEW QUESTIONS (Part 1)

Question-1 What is IP Routing ?

IP routing is the process of moving packets from one network to another network using routers.

 

Question-2 What is routing protocol ?

• A routing protocol is used by routers to dynamically find all the networks in the internetwork
• Routing protocol ensure that all routers have the same routing table. 
• Basically, a routing protocol determines the path of a packet through an internetwork.
• Routing protocol uses route update packets to update neighboring routers about the networks connected to all routers within the internetwork and route update packets are used to help build and maintain routing tables on each router.
• Examples of routing protocols are RIP, RIPv2, IGRP, EIGRP, BGP and OSPF. 

Question-3 What is routed protocol ?

• Once all routers know about all networks, a routed protocol can be used to send user data (packets) through the established enterprise. 
• Routed protocols are assigned to an interface 
• And determine the method of packet delivery. 
• Routed protocol uses data packets to transport user data through the internetwork. .
• Examples of routed protocols are IP and IPv6.

Question-4 What is data packet ?

• Data packets Used to transport user data through the internetwork. 
• Protocols used to support data traffic are called routed protocols.
• Examples of routed protocols are IP and IPv6.

Question-5 What is route update packet ?

• Route update packets Used to update neighboring routers about the networks connected to all routers within the internetwork. 
• Protocols that send route update packets are called routing protocols. Examples of some common ones are RIP, RIPv2,IGRP, EIGRP,OSPF, and BGP. 
• Route update packets are used to help build and maintain routing tables on each router.

Question-6 Which information are required for a router to route the packet ? 

• Destination address - Address in the routing table where router want to route the packet
• Neighbor routers from which it can learn about remote networks - Router learn about the remote network from neighboring router or administrator after that router builds the routing table which is also known as map of the inter network.
• Possible routes to all remote networks 
• The best route to each remote network
• How to maintain and verify routing information

Question-7 What is the routing table ?

Routing table describes how to find the remote networks. Routers use a routing table (map of the inter-network) to make path selections, and routing table is also used by router to forward packets to remote networks. Routing table containing the following information.

• Network addresses Protocol-specific network addresses. A router must maintain a routing table for individual routed protocol because each routed protocol keeps track of a network with a different addressing scheme like IPv4, IPv6, IPX
• Interface The exit interface used by a packet when packet destined for a specific network.  
• Metric The distance to the remote network. Different routing protocols use different method of calculating this distance like hop count, delay, bandwidth.

 

Question-8 If a router is not directly connected to a network then how can a router learn about the remote network ?

If a network is directly connected, then the router already knows how to get to it. But if the router is not directly connected to the network. the router must use one of two ways to learn how to get to the remote network: Static Routing and Dynamic Routing.

 

Question-9 What is static routing ?

• In static routing, Administrator is responsible to update all network location by hand into each router's routing table.
• If any changes occur in the network, the administrator is responsible to update all changes by hand into routing table of all routers.

 

Question-10 What are advantages and disadvantages of static routing

Advantages : -

• There is no overhead on the router CPU
• There is no bandwidth usage between routers
• It adds security because the administrator can choose to allow routing access to certain networks only.

Disadvantages : -

• The administrator must really understand the inter-network and how each router is connected in order to configure routes correctly.
• If a network is added to the inter-network, the administrator has to add a route to it on all routers—by hand.
• It’s not feasible in large networks because maintaining it would be a full-time job in itself

Question-11 How to configure static routing ?

Here’s the command syntax you use to add a static route to a routing table:

ip route [destination_network]  [mask]  [next-hop_address or exit interface]  [administrative_distance] [permanent]

This list describes each command in the string:

ip route - The command used to create the static route.

destination_network - Destination network from which you want to communicate.

mask - You would have to use mask with destination network.

next-hop_address - The address of the next-hop router that will receive the packet and forward it to the remote network. This is the IP address of a router interface which is directly connected to the router on which you are going to configure static route.

exit-interface - You can use exit interface at the place of next hop address, it is similar to next hop address and shows up as a  directly connected route.

administrative_distance -  By default, static routes have an administrative distance of 1 if you are using next hop address and 0 if you use an exit interface instead of a next-hop address. You can change the default value of administrative distance by adding an administrative weight at the end of the command.

permanent - If the interface is shut down or the router can’t communicate to the next- hop router, the route will automatically be discarded from the routing table by default. So if you are using  permanent command it will keep the entry in the routing table no matter what happens.

Take a look at a sample static route and see what we can find out about it.

ROUTER(config)#IP ROUTE      192.168.10.0      255.255.255.0       10.1.2.2         150   prmanent

IP route  - command tells us simply that it is a static route.

192.168.10.0 -  is the remote network we want to send packets to.

255.255.255.0 -  is the mask of the remote network.

10.1.2.2 -  is the next hop, or router, we will send packets to.
150 -  The 150 at the end changes the default administrative distance (AD) of 1 to 150. By default administrative distance of static route is 1 when we are using next hop address but in this example we set the AD 150.

One more example,
Router(config)#IP ROUTE           172.16.3.0             255.255.255.0          s0/0/0

S0/0/0 - This is exit interface, instead of using a next-hop address, we can use an exit interface that will make the route show up as a directly connected network. Functionally, the next hop and exit interface work exactly the same.

 

Question - 12 You must know these thing, when you are adding a static route on a router.

• You must be able to ping the router interface before you can successfully add the route. 
• If you type in the wrong next-hop address or the interface to that router is down, the static route will show up in the router’s configuration but not in the routing table.

 

Question-13 What is Dynamic routing ?

• In dynamic routing we use routing protocols to find networks and update routing tables on routers. 
• This is easier than using static or default routing, but it’ll cost you in terms of router CPU processing and bandwidth on the network links. 
• In dynamic routing, a protocol on one router communicates with the same protocol running on neighboring routers. 
• The routers then update each other about all the networks they know about and place this information into the routing table. 
• If a change occurs in the network, the dynamic routing protocols automatically inform all routers about the event.

 

Question-14 Can we use layer 2 switches as either a default gateway or another destination ?

No because switches have nothing to do with routing, it is layer 2 device

 

Question - 15 What is FCS (Frame Check Sequence) and it's role ?

Other Posts:-

OSI LAYERS AND FUNCTIONS
IP ROUTING BASIC
IP ROUTING SCENARIOS
RIP BASIC
RIP TROUBLESHOOTING
NETWORK COMMAND ISSUE
INTERFACE ISSUE
VERSION MISMATCH ISSUE
PASSIVE INTERFACE ISSUE
MAXIMUM HOP COUNT ISSUE
RIP OFFSET LIST CONFIGURATION
BGP - INTERVIEW QUESTIONS (Part - 1)
LAYER-2 SWITCHING

     

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Anubhav Upadhyay

Hello and welcome to networktopic Blog. My name is Anubhav. I am a Senior Network Egineer. I have created this blog specially to serve interview questions and answer on Network Routing and Switching, I will try my best to serve correct and updated networking knowledge for you as per my corporate experience.

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