Chapter 8 - IP Routing

Question 1

Describe the basic IP routing process.

Answer 1

You need to remember that the frame changes at each hop but that the packet is never changed or manipulated in any way until it reaches the destination device (the TTL field in the IP header is decremented for each hop, but that’s it!).

Question 2

List the information required by a router to successfully route packets.

Answer 2

To be able to route packets, a router must know, at a minimum, the destination address, the location of neighboring routers through which it can reach remote networks, possible routes to all remote networks, the best route to each remote network, and how to maintain and verify routing information.

Question 3

Describe how MAC addresses are used during the routing process.

Answer 3

A MAC (hardware) address will only be used on a local LAN. It will never pass a router’s interface. A frame uses MAC (hardware) addresses to send a packet on a LAN. The frame will take the packet to either a host on the LAN or a router’s interface (if the packet is destined for a remote network). As packets move from one router to another, the MAC addresses used will change, but normally the original source and destination IP addresses within the packet will not.

Question 4

View and interpret the routing table of a router.

Answer 4

Use the show ip route command to view the routing table. Each route will be listed along with the source of the routing information. A C to the left of the route will indicate directly connected routes, and other letters next to the route can also indicate a particular routing protocol that provided the information, such as, for example, R for RIP.

Question 5

Differentiate the three types of routing.

Answer 5

The three types of routing are static (in which routes are manually configured at the CLI), dynamic (in which the routers share routing information via a routing protocol), and default routing (in which a special route is configured for all traffic without a more specific destination network found in the table).

Question 6

Compare and contrast static and dynamic routing.

Answer 6

Static routing creates no routing update traffic and creates less overhead on the router and network links, but it must be configured manually and does not have the ability to react to link outages. Dynamic routing creates routing update traffic and uses more overhead on the router and network links.

Question 7

Configure static routes at the CLI.

Answer 7

The command syntax to add a route is: ip route [destination_network] [mask] [next-hop_address or exitinterface] [administrative_distance] [permanent].

Question 8

Create a default route.

Answer 8

To add a default route, use the command syntax: ip route 0.0.0.0 0.0.0.0 ip-address or exit interface type and number.

Question 9

Understand administrative distance and its role in the selection of the best route.

Answer 9

Administrative distance (AD) is used to rate the trustworthiness of routing information received on a router from a neighbor router. Administrative distance is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed via this route. All routing protocols are assigned a default AD, but it can be changed at the CLI.

Question 10

Differentiate distance-vector, link-state and hybrid routing protocols.

Answer 10

Distance-vector routing protocols make routing decisions based on hop count (think RIP), while link-state routing protocols are able to consider multiple factors such as bandwidth available and building a topology table. Hybrid routing protocols exhibit characteristics of both types.

Question 11

Configure RIP routing.

Answer 11

To configure RIP routing, first you must be in global configuration mode and then you type the command router rip. Then you add all directly connected networks, making sure to use the classful address and the version 2 command and to disable auto-summarization.

Question 12

At the appropriate command prompt, create a static route to network 172.16.10.0/ 24 with a next-hop gateway of 172.16.20.1 and an administrative distance of 150.

Answer 12

router (config) #ip route 172.16.10.0 255.255.255.0 172.16.20.1 150

Question 13

When a PC sends a packet to another PC in a remote network, what destination addresses will be in the frame that it sends to its default gateway?

Answer 13

It will use the gateway interface MAC at L2 and the actual destination IP at L3.

Question 14

At the appropriate command prompt, create a default route to 172.16.40.1.

Answer 14

router (config)# ip route 0.0.0.0 0.0.0.0 172.16.40.1

Question 15

On which type of network is a default route most beneficial?

Answer 15

Stub network

Question 16

At the appropriate command prompt, display the routing table on your router.

Answer 16

Router# show ip route

Question 17

When creating a static or default route, you don’t have to use the next-hop IP address; you can use the ___________________.

Answer 17

Exit interface

Question 18

True/ False: To reach a remote host, you must know the MAC address of the remote host.

Answer 18

False. The MAC address would be the router interface, not the remote host.

Question 19

True/ False: To reach a remote host, you must know the IP address of the remote host.

Answer 19

True.

Question 20

At the appropriate command prompt( s), prevent a router from propagating RIP information out serial 1.

Answer 20

router (config)# router rip

router (config-router)# passive-interface S1

Question 21

True/ False: RIPv2 is considered classless.

Answer 21

True.