EIGRP Router ID

EIGRP produces a Router ID, which is a 32-bit number in dotted decimal format. The Router ID (or RID) is used in external EIGRP to prevent routing loops. IN a properly configured network, the highest IP address assigned to a loopback address becomes the RID, and if no loopback interface is configured, the router's highest IP address becomes the RID. For an excellent explanation of the problem and configuration, look here.

Each router determines its RID when the process starts using the same general rules as OSPF:

1. The router will use a configured value (i.e. eigrp router-id a.b.c.d)
2. It will use the highest IPv4 address on an up/up loopback interface
3. It will then use the highest IPv4 address on an up/up non-loopback interface

The EIGRP RID has little value unless you are injecting external routes. That is when you are required to have unique RIDs to avoid confusion.

Show commands seldom list RID values, and are not needed to determine the topology database like OSPF. Duplicate RIDs will not prevent a neighbor relationship from taking place, either.