3.5.e Implement and troubleshoot EIGRP stub

3.5.e [i] Stub

The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network stability , reduces resource utilization , and simplifies stub router configuration.

Stub routing is commonly used in a hub and spoke network topology.

In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all non local traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table.
Generally, the distribution router need not send anything more than a default route to the remote router.

When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are propagated from the remote (stub) router, e.g. a stub router will not send dynamically learned prefixes to a hub router. The router responds to queries for summaries, connected routes, redistributed static routes, external routes , and internal routes with the message “inaccessible.” A router that is configured as a stub will send a special peer information packet to all neighboring routers to report its status as a stub router.

Any neighbor that receives a packet informing it of the stub status will not query the stub router for any routes, and a router (such as a hub) that has a stub peer will not query that peer. The stub router will depend on the distribution router to send the proper updates to all peers.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3188-3198).  . Kindle Edition.