EIGRP Stub Networks

A stub router indicates in it's hello packet, to let other routers know it is a stub router.

Q. Why use a EIGRP Stub?

A.
1. Limit amount of convergence traffic sent over links
2. Tell other routers you will NOT be a transit path for any additional networks. (eg. if a router is in active because it lost it's path, do not query me because I won't help you)
3. Avoid possible Stuck-In-Active scenarios

Typically, only remote routers are set as stubs, and only if they are single router sites. When a route goes down, stub routers ARE NOT QUERIED to find an alternate path, hub (regular neighbor routers) answer on behalf of the stub router.

*It is useful to note, stub features do not prevent other routers from advertising routes to the stub router.

Cisco defines a stub router as one which "core transit traffic should not flow"


Configure a router as a stub with the commands

eigrp stub [receive-only|connected|static|summary]

Any combination (other than receive-only) can be placed after the stub command.

The default is both connected and summary.

receive-only restricts the router from sharing any of it's routes with another router. When would you use this? If a router only has one interface in use, perhaps you have a router in place for the sole purpose of providing DHCP, VoIP gateway, or other services.

The connected, static, and summary commands are fairly self explanitory. Note that these must be in place AND the network command or redistribute command must be in use. Adding connected does not automatically add all connected routes to EIGRP, it only allows EIGRP to advertise them to neighboring routers if it is already in the routing table.

If a true stub network is desired, the hub (regular) router is typically configured to send a default route to the spoke (stub) routers so that only a single route is passed to them.