Verifying Enhanced IGRP Operation

The show ip eigrp neighbors EXEC-mode command is one of the main tools to use for EIGRP verification and maintenance. This command displays the contents of the EIGRP neighbor table and the peers that have been discovered . The EIGRP neighbor table contains the IP address of each neighbor, the local interface used for the connection, the holdtime value, the uptime value, and information regarding EIGRP packet updates, as shown in Listing 7.7.

Listing 7.7 A Sample Output from the show ip eigrp neighbors Command

 RouterA# show ip eigrp neighbors IP-EIGRP Neighbors for process 20 Address         interface    Holdtime   Uptime   Q     Seq     SRTT     RTO                              (secs)     (h:m:s)  Count Num     (ms)     (ms) 10.10.10.1      Ethernet1    9          0:00:33  0     13       6        22 10.10.20.2      Serial0      16         0:00:07  0     10       11       18 10.10.30.3      Ethernet0    12         0:00:09  0      6       3        8 

The eigrp log-neighbor-changes EXEC-mode command allows you to enable logging of status changes that occur with EIGRP adjacencies. It is also useful for monitoring router stability and issues surrounding SIA, as mentioned in the previous section.

The show ip route eigrp command is used to view the records currently in the EIGRP routing table. This command presents only the EIGRP-derived routes that are stored in the routing table, as shown in the following sample snippet:

 RouterA# show ip route eigrp D      10.0.0.0/8  [90/20268800] via 172.16.1.18, 00:00:22, Serial0/0        172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks D        172.16.1.20/30 [90/20268800] via 172.16.1.2, 00:00:22, Ethernet0/0 

The privileged show ip eigrp topology EXEC-mode command offers the contents of the EIGRP topology table, as shown in Listing 7.8. EIGRP maintains a separate topology table for each routable protocol that is configured on the router. The topology table contains a list of all successor and feasible successor routes, as well as the active or passive status.

Listing 7.8 A Sample Output from the show ip eigrp topology Command

 RouterA# show ip eigrp topology IP-EIGRP Topology Table for process 20 Codes: P  Passive, A  Active, U  Update, Q  Query, R  Reply,        r  Reply status P 172.16.90.0 255.255.255.0, 2 successors, FD is 0            via 172.16.80.28 (46251776/46226176), Ethernet0            via 172.16.81.28 (46251776/46226176), Ethernet1            via 172.16.80.31 (46277376/46251776), Ethernet0 P 172.16.81.0 255.255.255.0, 1 successors, FD is 307200            via Connected, Ethernet1            via 172.16.81.28 (307200/281600), Ethernet1            via 172.16.80.28 (307200/281600), Ethernet0            via 172.16.80.31 (332800/307200), Ethernet0 

The successor routes are listed with both the local router's calculated distance metric and the next hop router's calculated distance metric to the destination network. The local router's distance metric represents the best-known path to the destination network. This again is known as the router's feasible distance. The next -hop router's distance metric is the route's advertised distance. The routers are listed as passive (P) in the topology table in Listing 7.8 because the routes are operational and EIGRP is not "actively" looking for alternate paths to reach the destination network. If RouterA were to determine that the neighbor advertising the successor route was not functioning, the route would be listed as active (A) and the router would start the query process to probe other EIGRP neighbors for an alternate route to that particular network. The show ip eigrp topology command also shows the number of successors for each route entry.

The show ip eigrp traffic command is used to establish the amount of control packet traffic that an EIGRP router has received and transmitted. This command displays the number of Hello, update, query, reply, and ACK packets that were sent to or received by a router.

The show ip protocols command illustrates the parameters for all routing protocols that were configured for use on a router. It also shows the current state of the EIGRP process, if applicable . You can also use this command to quickly get the EIGRP AS number, as well as any filtering or distribution numbers , distance, and neighbor data.

Using the passive-interface command in router configuration mode enables the designated interface to accept incoming routing updates and prevents the specified interface from advertising all outgoing routing updates. This also serves to prevent the establishment of a neighbor adjacency . The syntax for the passive-interface command is

 RouterA(config-router)# passive-interface type number 

The type and number keywords indicate the interface type and number (for example, Ethernet 0/1). The no passive-interface type number command is used to re-enable route updates for a specific interface. Listing 7.9 shows the correct command for preventing RouterA from advertising EIGRP routes on interface e0/0 for AS 20:

Listing 7.9 A Sample Output from the passive-interface Command

 RouterA>en RouterA#config t Enter configuration commands, one per line. End with CNTL/Z RouterA(config)# router eigrp 20 RouterA(config-router)# network 172.16.1.0 RouterA(config-router)# passive-interface e0/0 RouterA(config-router)# exit RouterA(config)# 

Link-state protocols, such as OSPF and EIGRP, neither send nor receive any routing updates for interfaces configured as passive because neighboring routers that run link-state protocols cannot establish bidirectional communication by using the Hello protocol. Using the default keyword with passive-interface sets all active interfaces to passive mode. The default keyword will not re-enable all the interfaces automatically.

The privileged debug eigrp packets EXEC-mode command is used to establish and diagnose end-to-end connectivity problems, such as abnormal session closures between EIGRP neighbor routers. When used without parameters, the debug eigrp packets command displays information regarding all types of communication packets exchanged between the local router and its neighbors. You use the debug eigrp packets ? command to display a list of the packet types that are used by EIGRP. The ? parameter, used in conjunction with most IOS commands, displays content-sensitive help that demonstrates the 11 available parameters that can be used with this command. To display the individual packet types that are available for individual or group output, type the command shown in Listing 7.10.

Listing 7.10 The Results of the debug eigrp packets ? Command

 RouterA# debug eigrp packets ?   ack       EIGRP ack packets   hello     EIGRP hello packets   ipxsap    EIGRP ipxsap packets   probe     EIGRP probe packets   query     EIGRP query packets   reply     EIGRP reply packets   request   EIGRP request packets   retry     EIGRP retransmissions   terse     Display all EIGRP packets except Hellos   update    EIGRP update packets   verbose   Display all EIGRP packets   <cr> 

This display indicates the possible parameters and a brief description of the use of the parameter. Using the debug eigrp packets command with the verbose parameter would display traffic statistics for all EIGRP packets. The information derived from the debug eigrp packets verbose command can be used to diagnose end-to-end connectivity problems associated with the EIGRP neighbor routers.

Another command that you may want to use sparingly is the debug ip eigrp command. This prolific command generates a ton of valuable output about packets that are sent and received on an interface. The debug ip eigrp summary option generates a summary version of your EIGRP operations. This shows a similar result to the show ip protocols command.