Problem Isolation in IGRP
There are a number of commands available in the Cisco IOS with which to isolate and troubleshoot problems in IGRP networks. Table 7.3 lists the different show command options for IGRP.
| Show Command | Description |
|---|---|
| show ip route | Displays entries in the IP routing table for the router in which this command is issued. |
| show ip protocols | Displays filters, parameters, and network information details corresponding to the active routing protocol that is configured in the router. |
| show ip route igrp Number | Displays only IGRP routes in the routing table. It takes one parameter, Number, which is the number of the IGRP AS whose routes are being verified using this command. |
| show interface | Displays information about network interfaces within the IGRP network. |
| show running-config | Displays the current updated operating configuration for IGRP in the router where this command is issued. |
The show commands are used to verify the IGRP routing protocol configuration on a router. These commands verify the configuration or any customizations performed in IGRP networks. The output of show commands displays details of routing protocols that are configured in routers.
Table 7.4 lists different debug commands that are used for thorough packet level troubleshooting for problems in IGRP networks.
| Debug Command | Description |
|---|---|
| debug ip igrp transaction | Lists detailed contents of both sent and IGRP updates. |
| debug ip igrp events | Lists summary contents of both sent and received IGRP updates. Only shows the sending or receiving of IGRP packets and the number of routes in each update. |
| ping ip-addr/hostname | Tests the network connectivity with the specified network address. It accepts one parameter as ipaddress or host name of the router that we need to verify for network connectivity. This command sends test packets to the specified IP address or hostname and verifies the status of the network connectivity. |
| undebug all | Sets the IGRP debugging system off for the current router. |
Lists summary contents of both sent and received IGRP updates. Only shows the sending or receiving of IGRP packets and the number of routes in each update.
Tests the network connectivity with the specified network address. It accepts one parameter as ip-address or host name of the router that we need to verify for network connectivity. This command sends test packets to the specified IP address or hostname and verifies the status of the network connectivity.
Sets the IGRP debugging system off for the current router.
Consider the example depicted in Figure 7.1. Part of an IGRP network with five routers R1, R2, R3, R4, and R5 is connected as shown in the figure.
Figure 7.1: A network configured with the IGRP routing protocol.
In this IGRP scenario, R1 is connected to two other networks with IPs 11.0.1.0 and 11.0.2.0, respectively. R5 connects three networks, 10.0.1.0, 10.0.2.0, and 10.0.3.0.
In Figure 7.1, the show and debug commands are issued at R2. The configuration of R1 is shown in Listing 7.1.
Listing 7.1 Configuration of R1
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R1#conf t R1(config)#ip routing R1(config)#router igrp 100 R1(config-router)#network 11.0.1.0 R1(config-router)#network 11.0.2.0 R1(config-router)#exit R1(config)#interface ethernet 0 R1(config-if)#ip address 172.16.1.1 255.255.255.0 R1(config-if)#exit R1(config)#interface ethernet 1 R1(config-if)#ip address 172.16.2.1 255.255.255.0 R1(config-if)#exit R1(config)#exit R1
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The configuration of R2 is shown in Listing 7.2.
Listing 7.2 Configuration of R2
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R2#conf t R2(config)#ip routing R2(config)#router igrp 100 R2(config-router)#exit R2(config)#interface ethernet 0 R2(config-if)#ip address 172.16.1.2 255.255.255.0 R2(config-if)#exit R2(config)#interface ethernet 1 R2(config-if)#ip address 192.168.1.2 255.255.255.0 R2(config-if)#exit R2(config)#exit R2#
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The configuration of R3 is shown in Listing 7.3.
Listing 7.3 Configuration of R3
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R3#conf t R3(config)#ip routing R3(config)#router igrp 100 R3(config-router)#exit R3(config)#interface ethernet 0 R3(config-if)#ip address 192.168.1.1 255.255.255.0 R3(config-if)#exit R3(config)#interface ethernet 1 R3(config-if)#ip address 192.168.2.1 255.255.255.0 R3(config-if)#exit R3(config)#interface ethernet 2 R3(config-if)#ip address 192.168.3.1 255.255.255.0 R3(config-if)#exit R3(config)#exit R3#
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The configuration of R4 is shown in Listing 7.4.
Listing 7.4 Configuration of R4
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R4#conf t R4(config)#ip routing R4(config)#router igrp 100 R4(config-router)#exit R4(config)#interface ethernet 0 R4(config-if)#ip address 172.16.2.2 255.255.255.0 R4(config-if)#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#
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The configuration of R5 is shown in Listing 7.5.
Listing 7.5 Configuration of R5
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R5#conf t R5(config)#ip routing R5(config)#router igrp 100 R5(config-router)#network 10.0.1.0 R5(config-router)#network 10.0.2.0 R5(config-router)#network 10.0.3.0 R5(config-router)#exit R5(config)#interface ethernet 0 R5(config-if)#ip address 192.168.2.2 255.255.255.0 R5(config-if)#exit R5(config)#exit R5#
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Output of the show ip protocols command at R2 is as shown in Listing 7.6.
Listing 7.6 Output of the show ip protocols Command at R2
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R2#show ip protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 32 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 172.16.0.0 192.168.1.0 Routing Information Sources: 172.16.1.1 100 00:00:06 192.168.1.1 100 00:00:09 Distance: (default is 100)
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The output of the show ip route command for R2 is as shown in Listing 7.7.
Listing 7.7 Output of the show ip route Command at R2
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R2#sh 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 172.16.0.0 is subnetted, 2 subnets C 172.16.1.0/24 is directly connected, Ethernet0 I 172.16.2.0/24 [100/273] via 172.16.1.1, 00:08:23, Ethernet0 C 192.168.1.0/24 is directly connected, Ethernet1 I 11.0.0.0/8 [100/273] via 172.16.1.1, 00:04:20, Ethernet0 I 192.168.2.0/24 [100/273] via 192.168.1.1, 00:02:30, Ethernet1 I 192.168.3.0/24 [100/273] via 192.168.1.1, 00:06:32, Ethernet1 I 10.0.0.0/8 [100/437] via 192.168.1.1, 00:03:15, Ethernet1
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Output of the show ip route igrp command for R2 is as shown in Listing 7.8.
Listing 7.8 Output of the show ip route igrp Command at R2
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R2#show ip route igrp 100 Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 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 U - per-user static route, o - ODR Gateway of last resort is not set C 172.16.1.0/24 is directly connected, Ethernet0 C 192.168.1.0/24 is directly connected, Ethernet0
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The output of the debug ip igrp transactions command for R1 is as shown in Listing 7.9.
Listing 7.9 Output of the debug ip igrp transactions Command at R1
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R1#debug ip igrp transactions IGRP protocol debugging is on R1# IGRP: sending update to 255.255.255.0 via Ethernet0 (172.16.1.1) network 11.0.1.0, metric=8476 network 11.0.2.0, metric=8576 IGRP: sending update to 255.255.255.0 via Ethernet1 (172.16.2.1) network 11.0.1.0, metric=8476 network 11.0.2.0, metric=8576
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Output of the debug ip igrp events command for R2 is as shown in Listing 7.10.
Listing 7.10 Output of the debug ip igrp events Command at R2
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R2#debug ip igrp events IGRP event debugging is on R2# IGRP: sending update to 255.255.255.0 via Ethernet0 (172.16.1.2) IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. IGRP: Total routes in update: 2 IGRP: sending update to 255.255.255.0 via Ethernet1 (192.168.1.2) IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. IGRP: Total routes in update: 2
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Output of the ping ip-address command for R2 is as shown in Listing 7.11.
Listing 7.11 Output of the ping ip-address Command
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R2#ping 172.16.0.2 Sending 5, 64 byte ICMP echoes to 172.16.0.2, timeout is 2 seconds: 36 bytes from 172.16.0.2: icmp seq=0. time=0. ms 36 bytes from 172.16.0.2: icmp seq=1. time=0. ms 36 bytes from 172.16.0.2: icmp seq=2. time=0. ms 36 bytes from 172.16.0.2: icmp seq=3. time=0. ms 36 bytes from 172.16.0.2: icmp seq=4. time=0. Ms 100% success rate (5/5), round-trip min/avg/max = 0/0/0 ms
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The output of the undebug all command for R2 is as shown in Listing 7.12.
Listing 7.12 Output of the undebug all Command for R2
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R2#undebug all IGRP event debugging is off
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Misconfiguration in IGRP
Misconfiguration can be caused either by manual or system errors. You need to take care while configuring IGRP in a router, because even a small configuration error can affect the traffic of the whole network. Misconfiguration problems in IGRP can occur when:
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IGRP routes are missing from the routing table.
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IGRP is not installing all possible equal cost paths.
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ASN is misconfigured.
Misconfiguration in IGRP
IGRP routes may be missing from the routing table when:
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Network statement is missing or misconfigured.
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Layer 1 or 2 is down.
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Distribute list is blocking the route.
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Access list is blocking IGRP source address.
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Access list is blocking IGRP broadcast.
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Discontiguous network occurs.
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Invalid source of route.
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Switch, Frame Relay, and other Layer 2 media problems occur.
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AS mismatch of sender occurs.
Check the router configuration specific to routing. When a network command is added to the routing configuration of the router:
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The IGRP routing engine is activated to send and receive routing updates.
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The network is advertised in update packets.
Consider the example shown in Figure 7.1. The problems that arise when IGRP routes are missing from the routing table are:
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R1 is unable to ping any IP address.
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Delay in routing convergence.
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R1 is unable to reach any hosts in networks.
Unable to Ping IP Address
In Figure 7.1, R1 is unable to ping any IP address that belongs to network 10.0.0.0. Any hosts, including router interfaces, belonging to network 10.0.0.0 are unreachable from R1. Listing 7.13 shows the current state of the routing table of R1. This output is obtained by executing the sh ip route command.
Listing 7.13 Output of the sh ip route Command at R1
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R1#sh 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 11.0.0.0 is subnetted, 2 subnets C 11.0.1.0/24 is directly connected, Loopback1 C 11.0.2.0/24 is directly connected, Loopback2 172.16.0.0 is subnetted, 2 subnets C 172.16.1.0/24 is directly connected, Ethernet0 C 172.16.2.0/24 is directly connected, Ethernet1 I 192.168.1.0/24 [100/273] via 172.16.1.2, 00:05:21, Ethernet0 I 192.168.3.0/24 [100/273] via 172.16.2.2, 00:05:28, Ethernet1 I 192.168.2.0/24 [100/437] via 172.16.1.2, 00:01:36, Ethernet0
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Listing 7.13 shows that R1 does not have knowledge about networks 10.0.1.0, 10.0.2.0, and 10.0.3.0. This problem occurs because R1 is not receiving routing updates about the mentioned networks.
You must check if R5 is advertising the 10.0.0.0 network in the routing update. This is done by executing the show ip protocols command. Output of the show ip protocols command at R5 is as shown in Listing 7.14.
Listing 7.14 Output of the show ip protocols Command at R5
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R5#sh ip protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 44 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 192.168.2.0 Routing Information Sources: 192.168.2.1 100 00:00:03 Distance: (default is 100)
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In Listing 7.14, it’s clear that the IGRP in R1 is only active for network 192.168.2.0 and not for network 10.0.0.0. To troubleshoot this problem, the commands issued at R5 are:
R5#conf t R5(global)#router igrp 100 R5(global-router)#network 10.0.0.0
The new configuration can be checked using the show ip protocols command at R5, and the show ip route command at R1. Output of the show ip protocols command in R5 is as shown in Listing 7.15.
Listing 7.15 Output of the show ip protocols Command at R5
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R5#sh ip protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 44 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 10.0.0.0 192.168.2.0 Routing Information Sources: 192.168.2.1 100 00:00:03 Distance: (default is 100)
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Output of the show ip route command at R1 is as shown in Listing 7.16.
Listing 7.16 Output of the show ip route Command at R1
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R1#sh 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 11.0.0.0 is subnetted, 2 subnets C 11.0.1.0/24 is directly connected, Loopback1 C 11.0.2.0/24 is directly connected, Loopback2 172.16.0.0 is subnetted, 2 subnets C 172.16.1.0/24 is directly connected, Ethernet0 C 172.16.2.0/24 is directly connected, Ethernet1 I 192.168.1.0/24 [100/273] via 172.16.1.2, 00:05:21, Ethernet0 I 192.168.3.0/24 [100/273] via 172.16.2.2, 00:05:28, Ethernet1 I 192.168.2.0/24 [100/437] via 172.16.1.2, 00:01:36, Ethernet0 I 10.0.0.0/8 [100/437] via 172.16.1.2, 00:01:34, Ethernet0 [100/437] via 172.16.2.2, 00:02:42, Ethernet1
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Delay in Convergence
Sometimes, it may happen that configuration changes do not affect the routing tables. This problem is because of a delay in routing convergence. The router will send updates only after 90 seconds. To enforce an immediate effect on the routing table of a router, use the command clear ip route *. This command refreshes the current routing table.
Passive Interface
The configuration of passive interface in IGRP networks also causes the unavailability of routes. In Figure 7.1, R1 is unable to reach any hosts in networks 10.0.1.0, 10.0.2.0, and 10.0.3.0. This problem can be caused by the configuration of passive interface. The passive interface command prevents the interface from sending routing updates. However, this interface can access the routing update broadcasts on the link. It can also receive routing packets from other routers and accordingly modify the routing table.
Consider the example shown in Figure 7.2. The figure shows a network with passive interface configuration at R5.
Figure 7.2: An IGRP network showing passive interface configuration at R5.
In the IGRP scenario depicted in Figure 7.2, there are five routers: R1, R2, R3, R4, and R5. The interface that connects R1 and R2 has a bandwidth of 10 mbps. R1 is connected to two other networks with IPs 11.0.1.0 and 11.0.2.0. The interface between R1 and R4 has a bandwidth of 100 mbps. R2 is connected to R3, which in turn is connected to R4 using interfaces that have bandwidths 100 mbps each. R3 is connected to R5 using an interface with bandwidth 100 mbps. R5 is configured with a passive interface.
In Figure 7.2, R5 is configured with passive interface. The configuration of R5 is shown in Listing 7.17.
Listing 7.17 Configuration of R5
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R5#show run router igrp 100 network 192.168.2.0 network 10.0.0.0 passive-interface e0
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In Listing 7.17, the interface has been configured as passive. As a result, interface e0 of R5 will only be able to listen to the IGRP routing updates and hold all its outgoing IGRP routing updates via the configured interface.
If the interface is removed from passive mode, it will start sending its routing table to the neighboring routers and will reach R1. The routing table of R1 will be modified after receiving updates. R1 will now be able to reach any host in networks 10.0.1.0, 10.0.2.0, and 10.0.3.0. The no passive-interface command removes an interface from passive mode. The output of the no passive-interface command at R5 is shown in Listing 7.18.
Listing 7.18 Output of the no passive-interface Command at R5
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R5#conf t R5(config)#router rip R5(config-router)#no passive-interface e0
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IGRP Does Not Install All Possible Equal Cost Paths
This section will focus only on problems pertaining to equal cost paths. Equal cost path refers to multiple routes to a common destination with same metric values. By default, IGRP can use up to four equal cost paths. Misconfiguration can lead to missing of equal cost routes in the routing table. Consider the example depicted in Figure 7.3.
Figure 7.3: An IGRP routing scenario depicting equal cost paths.
In the IGRP scenario depicted in Figure 7.3, there are five routers: R1, R2, R3, R4, and R5. The interface that connects R1 and R2 has a bandwidth of 100 Mbps. R1 is connected to two other networks with IPs 11.0.1.0 and 11.0.2.0. The interface between R1 and R4 has a bandwidth of 100 mbps. R2 is connected to R3, which in turn is connected to R4 using interfaces that have bandwidths 100 mbps each. R3 is connected to R5 using an interface with bandwidth 100 mbps. R5 is configured with an active interface.
In Figure 7.3, R1 can reach networks 10.0.1.0, 10.0.2.0, and 10.0.3.0 via two paths:
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R1 to R2 to R3 to R5
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R1 to R4 to R3 to R5
Both paths have the same cost to the destination. Suppose the routing table of R1 shows only one path for the destination networks 10.0.1.0, 10.0.2.0, and 10.0.3.0. This scenario is shown in the output for the show ip route command at R1. Output for the show ip route command is shown in Listing 7.19.
Listing 7.19 Output of the show ip route Command at R1
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R1#sh 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 11.0.0.0 is subnetted, 2 subnets C 11.0.1.0/24 is directly connected, Loopback1 C 11.0.2.0/24 is directly connected, Loopback2 172.16.0.0 is subnetted, 2 subnets C 172.16.1.0/24 is directly connected, e0 C 172.16.2.0/24 is directly connected, e1 I 192.168.1.0/24 [100/273] via 172.16.1.2, 00:05:21, e0 I 192.168.3.0/24 [100/273] via 172.16.2.2, 00:05:28, e1 I 192.168.2.0/24 [100/437] via 172.16.1.2, 00:01:36, e0 I 10.0.0.0/8 [100/437] via 172.16.1.2, 00:01:34, e0
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To troubleshoot this problem, you need to understand the igrp updates that are being received by R1. Use the command debug ip igrp at R1 to see the routing updates. Output of the debug ip igrp command is as shown in Listing 7.20.
Listing 7.20 Output of the debug ip igrp Command at R1
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R1#debug ip igrp transactions IGRP protocol debugging is on R1# IGRP : sending update to 255.255.255.255. via e0 (172.16.1.1) network 11.0.1.0, metric=xxx network 11.0.2.0, metric=xxx IGRP : sending update to 255.255.255.255. via e1 (172.16.2.1) network 11.0.1.0, metric=xxx network 11.0.2.0, metric=xxx IGRP : received update from 172.16.1.2 on e0 network 192.168.1.0, metric xxx (neighbor xxx) network 192.168.2.0, metric xxx (neighbor xxx) network 192.168.3.0, metric xxx (neighbor xxx) network 10.0.0.0, metric xxx (neighbor xxx) IGRP : received update from 172.16.2.2 on e1 network 192.168.1.0, metric xxx (neighbor xxx) network 192.168.2.0, metric xxx (neighbor xxx) network 192.168.3.0, metric xxx (neighbor xxx) network 10.0.0.0, metric xxx (neighbor xxx)
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Listing 7.20 shows that R1 is receiving updates about network 10.0.0.0 from two different sources. Even after receiving the updates from two sources, R1 is registering it once. To troubleshoot this problem, look into the configuration of R1 using the show run command. The output of the show run command is shown in Listing 7.21.
Listing 7.21 Output of the show run Command at R1
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R1#show run router IGRP 100 network 172.16.0.0 network 11.0.0.0 maximum-path 1
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IGRP routers can install up to four equal cost paths to a common destination. In the scenario discussed, the router is configured to install only one route to a destination. Routers can be configured with the command maximum-path 1, when only one path is required for routing.
In the example depicted in Figure 7.3, the solution is to enter the command maximum-path 6 in R1 to maintain a maximum of six equal cost paths for a destination. R1 now shows two equal path cost routes for 10.0.0.0 networks. This can be verified by looking at the routing table of R1, as given in Listing 7.22.
Listing 7.22 Routing Table of R1
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R1#sh 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 11.0.0.0 is subnetted, 2 subnets C 11.0.1.0/24 is directly connected, Loopback1 C 11.0.2.0/24 is directly connected, Loopback2 172.16.0.0 is subnetted, 2 subnets C 172.16.1.0/24 is directly connected, e0 C 172.16.2.0/24 is directly connected, e1 I 192.168.1.0/24 [100/273] via 172.16.1.2, 00:05:21, e0 I 192.168.3.0/24 [100/273] via 172.16.2.2, 00:05:28, e1 I 192.168.2.0/24 [100/437] via 172.16.1.2, 00:01:36, e0 I 10.0.0.0/8 [100/437] via 172.16.1.2, 00:01:34, e0 [100/437] via 172.16.2.2, 00:02:42, e1
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Misconfigured ASN
Consider the example depicted in Figure 7.4. In the figure, there are two different ASs that run IGRP with ids 100 and 1000, respectively. There are five routers: R1, R2, R3, R4, and R5. R1, R2, R3, and R4 are in the same AS as id 100 whereas R5 is in a different AS with id 1000.The interface that connects R1 and R2 has a bandwidth of 10 mbps. R1 is connected to two other networks with IPs 11.0.1.0 and 11.0.2.0. The interface between R1 and R4 has a bandwidth of 100 mbps. R2 is connected to R3, which in turn is connected to R4 using interfaces that have bandwidths of 100 mbps each. R3 is connected to R5 using an interface with a bandwidth of 100 mbps. Three networks with network IDs 10.0.1.0, 10.0.2.0, and 10.0.3.0 are connected to R5.
Figure 7.4: An IGRP network showing mismatch in ASN.
In Figure 7.4, the routing table for R3 is shown in Listing 7.23.
Listing 7.23 Routing Table of R3
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R3#sh 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 192.168.1.0/24 is directly connected, Ethernet0 C 192.168.2.0/24 is directly connected, Ethernet1 C 192.168.3.0/24 is directly connected, Ethernet2 I 172.16.1.0/24 [100/273] via 192.168.1.2, 00:08:41, Ethernet0 I 11.0.1.0/24 [100/437] via 192.168.1.2, 00:07:37, Ethernet0 I 11.0.2.0/24 [100/437] via 192.168.3.2, 00:03:17, Ethernet2 I 172.16.2.0/24 [100/437] via 192.168.1.2, 00:03:18, Ethernet0
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In Listing 7.23, it is clear that the route information about network 10.0.0.0 is missing. The routing table of R5 is shown in Listing 7.24.
Listing 7.24 Routing Table of R5
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R5#sh 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, Loopback2 C 10.0.3.0/24 is directly connected, Loopback3 C 192.168.2.0/24 is directly connected, Ethernet0
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Listing 7.24 indicates that R5 is cut off from the network, because the routing table displays only information about the directly connected routes. This could happen if the routing process is disabled in R5 or if it is misconfigured, assuming that the connectivity is error free. Compare the configuration of R5 with that of other routers in the network. The configuration of R5 is as shown in Listing 7.25.
Listing 7.25 Configuration of R5
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R5#sh ip protocols Routing Protocol is "igrp 1000" Sending updates every 90 seconds, next due in 44 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 1000 Routing for Networks: 10.0.0.0 192.168.2.0 Routing Information Sources: 192.168.2.1 100 00:00:03 Distance: (default is 100)
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In Listing 7.25, the code highlighted in bold should be checked for the proper functioning of the routing protocol. The configuration of R5 is compared with that of R3. The configuration of R3 is as shown in Listing 7.26.
Listing 7.26 Configuration of R3
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R3#show ip protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 54 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 192.168.1.0 192.168.2.0 192.168.3.0 Routing Information Sources: 192.168.1.2 100 00:00:00 192.168.3.2 100 00:00:00 192.168.2.2 100 00:00:00 Distance: (default is 100)
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A comparison of the configuration of R5 with R3 shows that the IGRP routing process of R5 is using ASN 1000, and the routing process of R3 is using ASN 100. This is a mismatch caused by configuration error. Only those routers carrying the same ASN are allowed to share and exchange routing table information among them.
To troubleshoot this problem, reconfigure R5 by reenabling the IGRP routing process with the correct process id. Listing 7.27 displays the output of the routing protocol configuration of R5 with the correct process id.
Listing 7.27 Reconfiguring R5
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R5#conf t R5(config)#no router igrp 1000 R5(config)#router igrp 100 R5(config-router)#network 10.0.0.0 R5(config-router)#network 192.168.3.0 R5(config-router)#exit
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To confirm the correct functioning of the routers, check the routing tables of R3 and R5 using the show ip route command. The routing table of R3 is shown in Listing 7.28.
Listing 7.28 Routing Table for R3
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R3#sh 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 192.168.1.0/24 is directly connected, Ethernet0 C 192.168.2.0/24 is directly connected, Ethernet1 C 192.168.3.0/24 is directly connected, Ethernet2 I 172.16.1.0/24 [100/273] via 192.168.1.2, 00:08:41, Ethernet0 I 11.0.1.0/24 [100/437] via 192.168.1.2, 00:07:37, Ethernet0 [100/437] via 192.168.3.2, 00:03:17, Ethernet2 I 172.16.2.0/24 [100/437] via 192.168.1.2, 00:03:18, Ethernet0 I 10.0.0.0/8 [100/273] via 192.168.2.2, 00:01:27, Ethernet1
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The routing table of R5 is shown in Listing 7.29.
Listing 7.29 Routing Table for R5
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R5#sh 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, Loopback2 C 10.0.3.0/24 is directly connected, Loopback3 C 192.168.2.0/24 is directly connected, Ethernet0 I 192.168.1.0/24 [100/273] via 192.168.2.1, 00:05:31, Ethernet0 I 192.168.3.0/24 [100/273] via 192.168.2.1, 00:01:28, Ethernet0 I 172.16.0.0/16 [100/437] via 192.168.2.1, 00:09:34, Ethernet0 I 11.0.0.0/8 [100/437] via 192.168.2.1, 00:05:14, Ethernet0
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The routing tables of R3 and R5 show that all the routers—R1, R2, R3, R4, and R5—exchange routing table information. R3 can now learn the routes of network 10.0.0.0, and R5 can learn the routes that are connected to the other routers.
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