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 shows steps when Host A pings Host B (lots of steps!)

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 other Timeouts are common while routers add to cache Then, 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 Lab_A(config)# network 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 t 2. RouterA(config)#router rip 3. RouterA(config-router)#network 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 Check configurations (pp ) show ip route show protocols show ip protocol debug ip rip debug ip igrp events debug ip igrp transactions