User's Manual

Configuring EIGRP
EIGRP Configuration Task List
IPC-269
Cisco IOS IP Configuration Guide
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 will need to configure
summarization on the distribution routers.
Note When configuring the distribution router to send only a default route to the remote router, you must
use 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 will send a query
to the remote router even if routes are being summarized. If there is a problem communicating over the
WAN link between the distribution router and the remote router, an EIGRP stuck in active (SIA)
condition could occur and cause instability elsewhere in the network. The EIGRP Stub Routing feature
allows a network administrator to prevent queries from being sent to the remote router.
Dual-Homed Remote Topology
In addition to a simple hub-and-spoke network where a remote router is connected to a single
distribution router, the remote router can be dual-homed to two or more distribution routers. This
configuration adds redundancy and introduces unique issues, and the stub feature helps to address some
of these issues.
A dual-homed remote router will have two or more distribution (hub) routers. However, the principles
of stub routing are the same as they are with a hub-and-spoke topology. Figure 49 shows a common
dual-homed remote topology with one remote router, but 100 or more routers could be connected on the
same interfaces on distribution router 1 and distribution router 2. The remote router will use the best
route to reach its destination. If distribution router 1 experiences a failure, the remote router can still use
distribution router 2 to reach the corporate network.
Figure 49 Simple Dual-Homed Remote Topology
Figure 49 shows a simple dual-homed remote with one remote router and two distribution routers. Both
distribution routers maintain routes to the corporate network and stub network 10.1.1.0/24.
Corporate
network
Distribution
router 1
(hub)
Distribution
router 2
(hub)
Remote
router
(spoke)
10.1.1.0/24
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