Cisco Catalyst 4500 Series Software Configuration Manual page 943

Chapter 35 Configuring Layer 3 Interfaces
Configuring EIGRP Stub Routing
remote router must forward all nonlocal 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. The stub router responds to all 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 sends 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 does not query the stub router for any
routes, and a router that has a stub peer does not query that peer. The stub router depends on the
distribution router to send the proper updates to all peers.
Figure 35-4 shows a simple hub-and-spoke configuration.
Figure 35-4 Simple Hub-and-Spoke Network
Internet
Corporate
network
Distribution Remote
router router
(hub) (spoke)
The stub routing feature does not prevent routes from being advertised to the remote router. In the
example in Figure 35-4, the remote router can access the corporate network and the Internet using a
distribution router only. In this example, having a full route table on the remote router serves no purpose
because the path to the corporate network and the Internet always uses a distribution router. The larger
route table only reduces the amount of memory required by the remote router. Bandwidth and memory
can be conserved by summarizing and filtering routes in the distribution router. The remote router need
not receive routes that have been learned from other networks because the remote router must send all
nonlocal traffic, regardless of destination, to the distribution router. If a true stub network is desired, the
distribution router should be configured to send only a default route to the remote router. The EIGRP
stub routing feature does not automatically enable summarization on the distribution router. In most
cases, the network administrator needs to configure summarization on the distribution routers.
When configuring the distribution router to send only a default route to the remote router, you must use
Note
the ip classless command on the remote router. By default, the ip classless command is enabled in all
Cisco IOS images that support the EIGRP stub routing feature.
Without the stub feature, even after the routes that are sent from the distribution router to the remote
router have been filtered or summarized, a problem might occur. If a route is lost somewhere in the
corporate network, EIGRP could send a query to the distribution router, which in turn sends a query to
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
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