IP Routing

1
Chapter 5

• IP Routing

2
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

3
IP Routing Process

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

4
IP Routing Process (cont.)
5
IP Routing Process (cont.)
6
IP Routing in Larger Network

• Figure 5.2 shows diagram of network
• Table 5.1 shows networks, interfaces, and
  addresses
• Then, configure those routers!

7
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

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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

9
Verify Your Routing

• Ping from one end router to the other
• Timeouts are common while routers add to cache
• Then, connectivity should be quick

10
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

11
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)

12
Administrative Distances

• Rate the trustworthiness of routes

13
Classes of Routing Protocols

• Distance Vector
• Distance is hops to remote network
• Vector is direction to remote network
• Used by RIP and IGRP
• Link State and Hybrid
• Keeps track of directly attached neighbors,
  topology of entire network, builds routing tables
• OSPF and EIGRP (not covered yet)

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Distance-Vector Routing

• Do you know where RIP has problems?

15
Distance-Vector Start-up
16
Distance Vector Convergence
17
Routing Loops

• What if Network 5 goes down?
• Routing tables dont converge quickly, loops can
  occur between remote sites

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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 (dont wait for normal routing
  broadcast timer)
• Holddowns wait longer than normal before
  announcing that route is back up

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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

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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

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Configure RIP

• First, remove any static routes. Then,
• Lab_A(config) router rip
• Lab_A(config) network 192.168.10.0
• Lab_A(config) network 192.168.20.0
• Lab_A(config) Z
• Lab_A

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More RIP Stuff

• Verifying the RIP Routing Tables
• 2621A(config)sh ip route
• You dont want RIP broadcast to Internet
• Holding Down RIP Propagation
• RouterAconfig t
• RouterA(config)router rip
• RouterA(config-router)network 10.0.0.0
• RouterA(config-router)passive-interface serial 0

23
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

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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