Troubleshooting Eigrp Neighbor Relationships

The first step in the flow is to troubleshoot neighbor relationships. Figure 5-9 shows the steps for troubleshooting these issues.

Figure 5-9 Troubleshooting EIGRP Neighbor Issues

Figure 5-9 Troubleshooting EIGRP Neighbor Issues

Example 5-9 shows output from the show ip eigrp neighbors command, which indicates that a successful neighbor relationship exists with two routers.

Example 5-9 Confirming EIGRP Neighbor Relationships

RouterX# show ip eigrp neighbors

IP-EIGRP neighbors for process 100

Example 5-9 Confirming EIGRP Neighbor Relationships

RouterX# show ip eigrp neighbors

IP-EIGRP neighbors for process 100

H

Address

Interface

Hold Uptime

SRTT

RTO

Q

Seq

(sec)

(ms)

Cnt

Num

1

10.23.23.2

Se0/0/1

13 00:02:26

29

2280

0

15

0

10.140.1.1

Se0/0/0

10 00:28:26

24

2280

0

25

For EIGRP routers to form a neighbor relationship, both routers must share a directly connected IP subnet. A log message that displays that EIGRP neighbors are "not on common subnet" indicates that an improper IP address exists on one of the two EIGRP neighbor interfaces. Use the show interface interface command to verify the IP addresses.

In the output in Example 5-10, the interface address is 10.2.2.3/24.

Example 5-10 Confirming EIGRP Neighbor IP Address

RouterX# show ip interface fa0/0

FastEthernet0/0 is up, line protocol is up Internet address is 10.2.2.3/24 Broadcast address is 255.255.255.255 Address determined by setup command MTU is 1500 bytes Helper address is not set Directed broadcast forwarding is disabled Outgoing access list is not set Inbound access list is not set

The network command that is configured under the EIGRP routing process indicates which router interfaces will participate in EIGRP. The "Routing for Networks" section of the show ip protocols command indicates that the networks have been configured; any interfaces in those networks participate in EIGRP. In the output of Example 5-11, EIGRP is running on any interfaces that have an IP address on the 10.0.0.0 and 192.168.1.0 networks.

Example 5-11 Confirming Router Interface Participation in EIGRP Routing

RouterX# show ip protocols Routing Protocol is "eigrp 100"

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 EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 100 --output omitted -Maximum path: 4 Routing for Networks: 10.0.0.0 192.168.1.0 Routing Information Sources:

Gateway Distance Last Update

(this router) 90 00:01:08

Distance: internal 90 external 170

The show ip eigrp interfaces command can quickly indicate on which interfaces EIGRP is enabled and show how many neighbors can be found on each interface. In the output in

Example 5-12, no peers currently exist on the FastEthernet 0/0 interface, and one peer exists on the Serial 0/0/0 interface.

Example 5-12 Confirming EIGRP Status and Neighbors on an Interface

RouterX# show ip eigrp interfaces

IP-EIGRP interfaces for process 100

Xmit Queue

Mean

Pacing Time

Multicast

Pending

Int Peers

Un/Reliable

SRTT

Un/Reliable

Flow Timer

Routes

FaO/O @

0/0

O/1

O

0

SeO/O/O 1

0/0

38

552

0

EIGRP routers create a neighbor relationship by exchanging hello packets. Certain fields in the hello packets must match before an EIGRP neighbor relationship is established:

■ EIGRP autonomous system (AS) number

NOTE EIGRP K values are used in the EIGRP best-path selection process and are discussed in the Cisco CCNP curriculum.

You can use the debug eigrp packets command to troubleshoot when hello packet information does not match. In Example 5-13, a K value mismatch exists.

Example 5-13 Verifying EIGRP Hello Packet Mismatches RouterX# debug eigrp packets

Mismatched adjacency values

01:39:13: EIGRP: Received HELLO on Serial0/0 nbr 10.1.2.2

01:39:13:AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0 01:39:13: K-value mismatch

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