Statically Assigning EIGRP Neighbors

To reduce overhead of EIGRP multicast traffic, EIGRP allows neighbors to be specifically, or statically defined. This may be useful in an environment where you have a frame relay circuit with several PVCs, but you only want EIGRP to be configured on a couple routers. In a normal multicast configuration, the frame would be replicated to all PVCs and use precious bandwidth that is unnecessary. By statically configuring the intended neighbors, the EIGRP messages only go to the intended neighbors.

Cool.

Configuration of a static neighbor is pretty straight-forward, but again, as with all IOS configuration, knowing how and why things work makes the design and verification much easier. To configure a static neighbor, you would enter the router sub command context and assign the neighbor as such:

router eigrp 9
neighbor <ip_address_of_intended_neighbor> <outgoing_int_on_router>

Some things to note about the above commands:

• the ip address of the neighbor router must be from the subnet connected to the listed interface
• a "network" command is not required, because EIGRP will still advertise the subnet connected to that interface

To verify a static neighbor, we need to add "detail" to the end of our "show ip eigrp neighbors" command as in:

show ip eigrp neighbors detail

Without the detail command, IOS only shows that a neighbor is valid or not. Other interesting facts about statically assigning neighbors are that IOS disables all EIGRP broadcasts on an interface where a neighbor is statically assigned. There is no need to broadcast out that interface any longer since we're defining specific neighbor partnerships. As a result, any dynamically discovered neighbors will cease to work, and no new neighbors will be dynamically discovered.

Apply with caution, and always know what you're doing before you press "Enter."

EIGRP is fun...