Chapter 9

Default distance value: Static

1

Default Distance value: OSPF

110

Default distance value: RIP

120

What is the default time interval for RIP for exchanging routing tables

30 seconds. This results in slow route convergence, and if multiple routers are sharing RIP routes, there will be even longer convergence time.

Default distance value: EGRIP

90

Static Route

A data traffic route that has been manually entered into either a router's or a computer's routing table

Administrative Distance

A feature used by routers to select the best path when more than one path is available

Reliability

A measure of the reliability of the link, typically in terms of the amount of errors.

Metric

A numeric measure assigned to routes for ranking the routes best to worst; the smaller the number, the better.

RIP does not support router authentication:

As a result, this can be exploited as vulnerability.

This table shows the connected networks, but RIP (R) is not enabled for any networks. Why?

At this point, RIP has been enabled only on RouterA in the campus network. RouterB and RouterC also need to have RIP enabled.

Bandwidth

Having to do with the data capacity of the networking link. A Fast-Ethernet 100Mbps link has greater data capacity than a 10Mbps Ethernet link.

Load

Having to do with the network activity on a link or router.

Examples of route metrics

Hop count Reliability Bandwidth Delay Cost Load Ticks

RIP is a classful routing only protocol:

It therefore does not support VLSM and CIDR. This prevents it from being the routing protocol of choice when having to deal with different sized subnets in a network.

show ip route static (sh ip route static)

Limits the routes displayed to only static

also called shortest-path first protocols

Link state protocols

contiguous networks

Meaning the networks and routes must have the same class network address (RIP can be used only in contiguous networks)This means the router addresses for the network connecting the routers must be the same class as the LAN connected to the router.

RIP has a hop count limit of 15:

Means a destination that is 15 hops away is considered to be unreachable.

areas

OSPF uses the concept of areas to partition a large network into smaller networks. The advantage of this is that the routers have to calculate routes only for their area. If a route goes down in a given area, only the routers in that area have to calculate new routes.

Four key issues are associated with dynamic routing protocols

Path determination Metric Convergence Load balancing

When do routers send Routing Tables?

RIP and other distance vector routing protocols send the entire routing table to neighbor routers at regular time intervals. Sometimes the routing tables can be quite large and the transfer can consume network bandwidth.

RIP uses hop count as a metric:

RIP determines the best route by counting the number of hops to reach the destination. A lower hop count wins over the higher hop count. This is a disadvantage when dealing with different bandwidth between hops. RIP does not take into consideration whether the higher hop count route might have higher bandwidth. Therefore, the lower bandwidth route could be taken.

What is the ideal size network for RIP

RIP is a relatively simple routing protocol to configure. However, RIP is good only for very small networks that have a limited staff size to manage the network and is not suited for networks that need fast convergence.

Configuring the static routes

Router#conf t Router(config)#int fa0/1 Router(config-if)#ip address 10.10.200.1 255.255.255.0 Router(config-if)#no shut Router(config)#int fa0/2 Router(config-if)#ip address 10.10.100.1 255.255.255.0 Router(config-if)#no shut

Save changes to the router configuration

Router#copy run start Router#wr m

The command structure for ip route is

Router(config)#ip route <destination> <subnet mask> <next hop>

how to initialize RIP

Router(config)#router rip Router(config-router)#network 10.0.0.0

how to initialize RIP and how to set the networks attached to the router

Router(config)#router rip Router(config-router)#network 10.0.0.0

configure RIPv2

RouterA(config)#router rip RouterA(config-router)#version 2

Variable Length Subnet Masking

Routes can be configured using different subnet masks

When do routing loops occur?

Routing loops occur when a router forwards packets back to the router that sent them

Gateway of Last Resort

The IP address of the router in your network where data packets with unknown routes should be forwarded

How to enable RIP protocol

The RIP routing protocol is enabled on the router by entering the command router rip at the Router(config)#

copy run start

The command for copying the running-configuration to the startup-configuration

show running-config (sh run)

The command that displays the router's running-configuration

show startup-config (sh start)

The command that displays the router's startup-configuration

show ip route (sh ip route)

The command that displays the routes and the routing address entry into the routing table

write memory (wr m)

The command that saves your configuration changes to memory. This is the same as issuing the copy run start command, which is the most common command for saving your configuration.

netstat -r

The command used to obtain the routing table for a host PC computer

Loopback

The data is routed directly back to the source

Link State Advertisement (LSA)

The exchange of updated link state information when routes change. Every time LSAs are sent, each router must recalculate the routing table.

Ticks

The measured delay time in terms of clock ticks, where each tick is approximately 55 milliseconds (1⁄18 second).

Classful Addressing

The network portion of a particular network address

Class Network Address

The network portion of the IP address based on the class of the network

Hop count

The number of routers the data packet must pass through to reach the destination network.

routing table code S

The router code for a static route

routing table code C

The router code for specifying a directly connected network

ip route

The router configuration command for manually setting the next hop IP address

How does the router update their routing tables in dynamic routing?

The routers update their routing tables using information obtained from adjacent routers.

What is the routing protocol responsible for?

The routing protocol is responsible for managing the exchange of routing information between the routers, and the choice of protocol defines how the routing information is exchanged and used.

Dynamic Routing Protocols

The routing table is dynamically updated to account for loss or changes in routes or changes in data traffic

Advertise

The sharing of route information

Two types of internal dynamic routing protocols

distance vector link state

Link state protocols

establish a relationship with a neighboring router. The routers exchange link state advertisements to update neighbors regarding route status. The link state advertisements are sent only if there is a change or loss in the network routes and the link state protocols converge to route selection quickly.

Open Shortest Path First (OSPF)

is a dynamic routing protocol, classified as a link state protocol

Routing Information Protocol (RIP)

is a dynamic routing protocol, meaning the routers periodically exchange routes. RIP is classified as a distance vector protocol using router hop count as the metric. RIP permits a maximum of 15 hops to prevent routing loops.

show ip protocol (show ip protocol)

is used to display the routing protocols running on the router, as shown. This command will display protocol information only after the routing protocol has been enabled and the network addresses are specified.

What happens when the neighboring router receives the table

it assigns a distance vector number to each route. The distance vector number is typically specified by some metric such as hop count.

The most common static route used in a host computer is

the default gateway

Delay

The time it takes for a data packet to travel from source to destination.

"Hello" Packets

Used in the OSPF protocol to verify that the links are still communicating

Load balancing

A procedure in the protocol that enables routers to use any of the multiple data paths available from multiple routers to reach the destination.

Path determination

A procedure in the protocol that is used to determine the best route.

Cost

A value assigned by the routing protocol or the network administrator to the link or the interface. Typically, the value is based on the referenced bandwidth.

Convergence

This happens when a router obtains a clear view of the routes in a network. The time it takes for the router to obtain a clear view is called the convergence time.

Gateway of last resort is not set

This means the router does not know how to route a data packet with a destination IP address that differs from the routes stored in the routing table. This will result in the router dropping the packet to the destination IP address. Without the gateway of last resort, a router will drop any data packets with destination networks that are not in its routing table.

The default gateway specifies which of the following?

Where the data is to be sent when the destination address for the data is not in the same subnet or is unknown

distance vector protocol

a routing algorithm that periodically sends the entire routing table to its neighboring or adjacent router

The main advantages of OSPF

are rapid convergence and the consumption of very little bandwidth. When a network is completely converged, all the routers in the network agree on the best routes.

classful addressing

class network address or classful address is the network portion of the address for the particular class of the network

Which of the following is the generic command for configuring a static route?

router(config)# ip route <destination ip address> <subnet mask> <next hop ip address>

What kind of protocol is RIP

standard protocol, not a proprietary protocol—meaning the use of the protocol is not limited to certain equipment manufacturers.

Why are subnet mask not classifies in RIP command

subnet masks are not specified in the RIP network command because the class network address is used and all IP addresses in the network (for example, 10.0.0.0) are enabled to use RIP.

The key issues of link state protocols are summarized as follows:

• Finds neighbors/adjacencies • Uses route advertisements to build routing table • Sends "Hello" packets • Sends updates when routing changes