EIGRP summarization

EIGRP summarization
The time needed for convergence can be decreased for EIGRP by reducing the number of routing
advertisements within a portion of your network, which promotes network stability. EIGRP has
added the concept of stub routing, but it is different than an OSPF stub area. This feature is used to
limit the number of query packets that need to be sent and tracked when a route is removed from
the topology table. When a route goes missing from the topology table, EIGRP marks it as active and
sends out query messages to its neighbors to see if they have a route to the network. This continues
until every router is contacted, and if a query packet gets lost or a neighbor is unreachable, the route
can become stuck in active (SIA), which is a bad thing to happen. An EIGRP router does not send
these messages to neighbors on networks when the router is configured as a stub, which decreases
the amount of time needed to reconcile an active route.
Multi-access interfaces, such as Ethernet and frame relay, are supported by EIGRP stub routing
only when all routers on that interface’s segment, except the central distribution hub router
to which all the stub routers direct their traffic, are configured as stub routers.