Chapter 5

IP Routing

Routing

Sending packets through network from one device to another

What must routers know?– Destination address– Neighboring routers– Possible routes to remote network– Best route to remote network– How to keep routing information current

IP Routing Process

Pages 207-210 shows steps when Host A pings Host B (lots of steps!)

IP Routing Process (cont.)

IP Routing Process (cont.)

IP Routing in Larger Network

Figure 5.2 shows diagram of network Table 5.1 shows networks, interfaces, and

addresses Then, configure those routers!

IP Routing in Our Network

Routing tables keep track of networks If destination is not in routing table, packet is

dropped! Must build routing table and keep it current Types of routing

– Static– Default– Dynamic

Static Routing

Admin manually adds routes to tables No overhead on router CPU, no overhead traffic

between routers, very secure Big pain to add routes often, not good for large or

changing networks Adding a static route:

ip route [destination_network] [mask] [next_hop_address or exitinterface] [administrative_distance] [permanent]

Verify Your Routing

Ping from one end router to the otherTimeouts are common while routers

add to cacheThen, connectivity should be quick

Default Routing

Only one exit port out of a stub network? Can set a default route

Routers Lab_A and Lab_C qualify Need to remove static routes and add one

default route

Dynamic Routing

Use protocols to automatically update tables Types of routing protocols for Ch. 5:

– Routing Information Protocol (RIP)– Interior Gateway Routing Protocol (IGRP)

Advanced protocols not covered here:– Enhanced Interior Gateway Routing Protocol

(EIGRP)– Open Shortest Path First (OSPF)

Administrative Distances

Rate the trustworthiness of routes

Classes of Routing Protocols

1. Distance Vector– Distance is hops to remote network– Vector is direction to remote network– Used by RIP and IGRP

2. Link State and Hybrid– Keeps track of directly attached neighbors,

topology of entire network, builds routing tables– OSPF and EIGRP (not covered yet)

Distance-Vector Routing

Do you know where RIP has problems?

Distance-Vector Start-up

Distance Vector Convergence

Routing Loops

What if Network 5 goes down? Routing tables don’t converge quickly, loops

can occur between remote sites

Stopping Routing Loops

Maximum hop count – avoids routers sending packets infinite times

Split Horizon – routing info cannot be sent back to where it was received

Route Poisoning – send immediate message that route is down (don’t wait for normal routing broadcast timer)

Holddowns – wait longer than normal before announcing that route is back up

RIP

A true distance-vector protocol– Sends updates every 30 seconds on all active

interfaces– Only uses hop count

Maximum allowable hop count of 15

Good for small networks– Inefficient on large networks or slow WAN links– RIP v1 requires same subnet mask for all devices

RIP

RIP Timers– Route update timer – usually 30 seconds– Route invalid timer – no message from router for 90

seconds? Route marked as invalid– Route flush timer – 240 seconds and still no word?

Remove route from table

Configure RIP

First, remove any static routes. Then,

1. Lab_A(config)# router rip

2. Lab_A(config)# network 192.168.10.0

3. Lab_A(config)# network 192.168.20.0

4. Lab_A(config)# ^Z

5. Lab_A#

More RIP Stuff

Verifying the RIP Routing Tables– 2621A(config)#sh ip route

You don’t want RIP broadcast to Internet– Holding Down RIP Propagation

1. RouterA#config t2. RouterA(config)#router rip3. RouterA(config-router)#network 10.0.0.04. RouterA(config-router)#passive-interface serial 0

Interior Gateway Routing Protocol (IGRP)

Cisco-only protocol for larger networks Max hop count of up to 255 Looks at hop count, bandwidth, and delays IGRP timers work on larger networks

– Update timers – 90 seconds– Invalid timers – 270 seconds– Holddown timers – 280 seconds– Flush timers – 630 seconds

Configure and Verify IGRP

Use same number for routers on same network IGRP Routing (e.g. 10)

Lab_A(config)#router igrp 10

Lab_A(config-router)#network 192.168.10.0

Check configurations (pp. 239-245)show ip route

show protocols

show ip protocol

debug ip rip

debug ip igrp events

debug ip igrp transactions