© 2002, Cisco Systems, Inc. All rights reserved. 1

Routing Overview

•To route, a router needs to do the following:• Know the destination address• Identify the sources it can learn from• Discover possible routes• Select the best route• Maintain and verify routing information

What Is Routing?

• Routers must learn destinations that are not directly connected.

What Is Routing? (Cont.)

• Static Route– Uses a route that a

network administrator enters into the router manually

•Dynamic Route–Uses a route that a

network routing protocol adjusts automatically for topology or traffic changes

Identifying Static and Dynamic Routes

Static Routes

• Configure unidirectional static routes to and from a stub network to allow communications to occur.

– Defines a path to an IP destination network or subnet or host

Router(config)#ip route network [mask] {address | interface}[distance] [permanent]

Static Route Configuration

Static Route Example

• This is a unidirectional route. You must have a route configured in the opposite direction.

Default Routes

• This route allows the stub network to reach all known networks beyond router A.

Verifying the Static Route Configuration

router#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route Gateway of last resort is 0.0.0.0 to network 0.0.0.0  10.0.0.0/8 is subnetted, 1 subnetsC 10.1.1.0 is directly connected, Serial0S* 0.0.0.0/0 is directly connected, Serial0

• Routing protocols are used between routers to determine paths and maintain routing tables.

• Once the path is determined, a router can route a routed protocol (IP).

What Is a Routing Protocol?

• An autonomous system is a collection of networks under a common administrative domain.

• IGPs operate within an autonomous system.

• EGPs connect different autonomous systems.

Autonomous Systems: Interior or Exterior Routing Protocols

Classes of Routing Protocols

© 2002, Cisco Systems, Inc. All rights reserved. 13

Distance Vector Routing

• Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.

Distance Vector Routing Protocols

•Updates proceed step-by-step from router to router.

Maintaining Routing Information

16

RIP

Metric

Metric

• Is a value that assign to each path

• Use to calculate with path is the best path to remote destination network

• Different in routing protocol

• The route with the lowest metric is the best route

Hop Count is metric in RIP Routing

– Maximum is 6 paths (default = 4)– Hop-count metric selects the path– Routes update every 30 seconds

RIP Overview

RIP Table

Load Balancing with RIP

By default, on a Cisco router, if multiple equal-cost paths existup to six entries are placed into the forwarding database and the routersload balance between them.

– Defines an IP routing protocol

Router(config)#router protocol [keyword]

• Mandatory configuration command for each IP routing process

• Identifies the physically connected network that routing updates are forwarded to

Router(config-router)#network network-number

Dynamic Routing Configuration

– Starts the RIP routing process

Router(config)#router rip

Router(config-router)#network network-number

• Selects participating attached networks

• Requires a major classful network number

RIP Configuration

RIP Configuration Example

Verifying the RIP Configuration

Displaying the IP Routing Table

debug ip rip Command

Summary– RIP is a distance vector routing protocol that uses hop

count as the metric for route selection and broadcasts routing updates every 30 seconds.

– To enable a dynamic routing protocol, you will select the routing protocol and then assign IP network numbers.

– The router rip command specifies RIP as the routing protocol. The network command identifies a participating attached network.

– The show ip commands display information about routing protocols and the routing table.

– Use the debug ip rip command to display information on RIP routing transactions.

Router RIP Example

S0 : 192.168.1.1

S1 : 192.168.3.1

F0/0 : 192.168.2.1

S0 : 192.168.3.2

S1 : 192.168.4.1

S0 : 192.168.4.2

S0 : 192.168.9.2

S0 : 192.168.7.2

S1 : 192.168.7.1S1 : 192.168.9.1

S1 : 192.168.1.2

F0/0 : 192.168.10.1

F0/0 : 192.168.5.1 F0/0 : 192.168.6.1 F0/0 : 192.168.8.1

Configure RIP

1. Assign ip to interface

2. Configure RIP Routing

3. Ping

4. Trace route

5. Show routing table

Verifying the RIP Configuration

Displaying the IP Routing Table

debug ip rip Command

Key Elements of RIP

– Hop count is the metric for path selection.– Maximum hop count of 15– 16 hops is considered infinity– By default, routing updates are broadcast

every 30 seconds.– Capable of load balancing

37

IGRP

Interior gateway routing protocol))

• This is helpful in larger networks and solves the problem of 15 hops being the maximum possible in a RIP network

Complex Metrics

MTU

Bandwidth

1

2 3

4

Delay of line

amount of time necessary to move a packet transmition from source to destination.

1 mb/s 1 mb/s

2 mb/s2 mb/s

Reliability

2 mb/s 2 mb/s

2 mb/s2 mb/s

Load

1 mb/s 1 mb/s

2 mb/s2 mb/s

MTU

• MTU : Maximum Transmission Unit

-The Maximum Packet size, in byte , that a particular interface can handle.

- The default MTU value on Ethernet interface is 1500 byte.

IGRP metric calculation

• By default IGRP chooses a route based on

Bandwidth and delay

Metric = bandwidth + delay

–Maximum 6 paths (default = 4)

–Within metric variance

–Next-hop router closer to destination

IGRP Unequal Multiple Paths

Configuring IGRP

Router(config-router)#network network-number

• Selects participating attached networks

Router(config)#router igrp autonomous-system

• Defines IGRP as the IP routing protocol

Verifying the IGRP Configuration

debug ip igrp transaction Command

debug ip igrp events Command

RouterA#debug ip igrp eventsIGRP event debugging is onRouterA#00:23:44: IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1)00:23:44: IGRP: Update contains 0 interior, 2 system, and 0 exterior routes.00:23:44: IGRP: Total routes in update: 200:23:44: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1)00:23:45: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes.00:23:45: IGRP: Total routes in update: 100:23:48: IGRP: received update from 10.1.1.2 on Serial200:23:48: IGRP: Update contains 1 interior, 1 system, and 0 exterior routes.00:23:48: IGRP: Total routes in update: 2

Displaying the IP Routing Table

Updating Routing Information Example

Updating Routing Information Example (Cont.)

Updating Routing Information Example (Cont.)

Updating Routing Information Example (Cont.)

Router IGRP Example

S0 : 192.168.1.1

S1 : 192.168.3.1

F0/0 : 192.168.2.1

S0 : 192.168.3.2

S1 : 192.168.4.1

S0 : 192.168.4.2

S0 : 192.168.9.2

S0 : 192.168.7.2

S1 : 192.168.7.1S1 : 192.168.9.1

S1 : 192.168.1.2

F0/0 : 192.168.10.1

F0/0 : 192.168.5.1 F0/0 : 192.168.6.1 F0/0 : 192.168.8.1

Configure IGRP

1. Assign ip to interface

2. Configure RIP Routing

3. Ping

4. Trace route

5. Show routing table