Cisco IP Routing Protocols(c) Trouble Shooting Techniques
Authors: Anand V.,  Chakrabarty K.
 Published year: 2006
 Pages: 50-52/130
Buy this book on amazon.com >>

Case Study

Consider the scenario depicted in Figure 7.6. There are four routers—R2, R3, R4, and R5—in the same IGRP AS. R4 has networks connected to it with network ids 10.0.1.0, 10.0.2.0, and 10.0.3.0.

click to expand
Figure 7.6: An IGRP case study.

In Figure 7.6, the configuration of R4 is as shown in Listing 7.32.

Listing 7.32 Configuration of R4

start example 
R4#conf t R4(config)#ip routing R4(config)#router igrp 100 R4(config-router)#network 10.0.1.0 R4(config-router)#network 10.0.3.0 R4(config-router)#exit R4(config)#interface ethernet 1 R4(config-if)#ip address 192.168.3.2 255.255.255.0 R4(config-if)#exit R4(config)#exit R4#
end example

The problem is that routing packets are not reaching R4 from network 10.0.2.0, which is connected to R4. To troubleshoot this problem, verify the IP route in R4 using the show ip route command. This command output shows only two network ids connected. The third network with network id 10.1.2.0 is not connected. The output of the show ip route command is shown in Listing 7.33.

Listing 7.33 Output of the show ip route Command

start example 
R4#show ip route Codes: 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 not set C 10.0.1.0/24 is directly connected, Loopback1 C 10.0.3.0/24 is directly connected, Loopback3 C 192.168.3.1/24 is directly connected, Ethernet0
end example

Reconfigure R4 with the configuration for network 10.1.2.0 as shown in Listing 7.34.

Listing 7.34 Reconfiguration of R4

start example 
R4#conf t R4(config)#ip routing R4(config)#router igrp 100 R4(config-router)#network 10.0.1.0 R4(config-router)#network 10.1.2.0 R4(config-router)#network 10.0.3.0 R4(config-router)#exit R4(config)#interface ethernet 1 R4(config-if)#ip address 192.168.3.2 255.255.255.0 R4(config-if)#exit R4(config)#exit R4#
end example

Verify routing information again using the show ip route command. The output for the command is shown in Listing 7.35.

Listing 7.35 Output of the show ip route Command

start example 
R4#show ip route Codes: 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 not set C 10.0.1.0/24 is directly connected, Loopback1

C 10.0.2.0/24 is directly connected, Loopback1

C 10.0.3.0/24 is directly connected, Loopback3 C 192.168.3.1/24 is directly connected, Ethernet0
end example

In Listing 7.35, the text in bold shows that network 10.0.2.0 is correctly configured.

Now all networks connected to R4 are correctly configured, and routing updates are sent properly to R4.



Summary

In this chapter, we learned about troubleshooting IGRP environments, which included problem isolation in IGRP environments. We also reminded you about resolution of problems in IGRP environments. In the next chapter, we move on to troubleshooting EIGRP routing environments.



Points to Remember

  • IGRP uses a composite metric that is calculated by a combination of delay, bandwidth, reliability, load, and MTU.

  • The show ip route command displays entries in the IP routing table for the router in which this command is issued.

  • The show ip protocols command displays filters, parameters, and network information details corresponding to the active routing protocol configured in the router.

  • The show ip route igrp Number command displays only the IGRP routes in the routing table.

  • The show interface command displays information about network interfaces within the IGRP network.

  • The show running-config command displays the current updated operating configuration for IGRP in the router where this command is executed.

  • The debug ip igrp transaction command lists detailed contents of both sent and received IGRP updates.

  • The debug ip igrp events command lists summary contents of both sent and received IGRP updates.

  • The ping ip-addr/hostname command tests the network connectivity with a specified network address.

  • The undebug all command sets the IGRP debugging system off for the current router.

  • Misconfiguration problems in IGRP can occur when IGRP routes are missing from the routing table, IGRP is not installing all possible equal cost paths, or if ASN is misconfigured.

  • The clear ip route * command refreshes the current routing table.

  • The passive interface command prevents the interface from sending routing updates.

  • Equal cost path refers to multiple routes to a common destination with same metric values.


Cisco IP Routing Protocols(c) Trouble Shooting Techniques
Authors: Anand V.,  Chakrabarty K.
 Published year: 2006
 Pages: 50-52/130
Buy this book on amazon.com >>

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