Cisco NCS 6000 Series User Manual

advertises this route to Router-B. Router-B is configured so that only a default summary route is advertised
to Router-C. The default summary route is applied to interface 0/1 on Router-B with the following configuration:
RP/0/RP0/CPU0:router(config)# router eigrp 100
RP/0/RP0/CPU0:router(config-eigrp)# address-family ipv4
RP/0/RP0/CPU0:router(config-eigrp-af)# interface GigabitEthernet 0/3/0/0
RP/0/RP0/CPU0:router(config-eigrp-af-if)# summary-address 100.0.0.0 0.0.0.0
Figure 11: Floating Summary Route Is Applied to Router-B
The configuration of the default summary route on Router-B sends a 0.0.0.0/0 summary route to Router-C
and blocks all other routes, including the 10.1.1.0/24 route, from being advertised to Router-C. However, this
configuration also generates a local discard route on Router-B, a route for 0.0.0.0/0 to the null 0 interface with
an administrative distance of 5. When this route is created, it overrides the EIGRP learned default route.
Router-B is no longer able to reach destinations that it would normally reach through the 0.0.0.0.0/0 route.
This problem is resolved by applying a floating summary route to the interface on Router-B that connects to
Router-C. The floating summary route is applied by relating an administrative distance to the default summary
route on the interface of Router-B with the following statement:
RP/0/RP0/CPU0:router(config-if)# summary-address 100 0.0.0.0 0.0.0.0 250
The administrative distance of 250, applied in the above statement, is now assigned to the discard route
generated on Router-B. The 0.0.0.0/0, from Router-A, is learned through EIGRP and installed in the local
routing table. Routing to Router-C is restored.
If Router-A loses the connection to Router-B, Router-B continues to advertise a default route to Router-C,
which allows traffic to continue to reach destinations attached to Router-B. However, traffic destined for
networks to Router-A or behind Router-A is dropped when the traffic reaches Router-B.
Figure 12: Floating Summary Route Applied for Dual-Homed Remotes, on page 186 shows a network with
two connections from the core: Router-A and Router-D. Both routers have floating summary routes configured
on the interfaces connected to Router-C. If the connection between Router-E and Router-C fails, the network
continues to operate normally. All traffic flows from Router-C through Router-B to the hosts attached to
Router-A and Router-D.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
185
Implementing EIGRP
Floating Summary Routes for an EIGRP Process

Cisco NCS 6000 Series Specifications

General

Brand	Cisco
Model	NCS 6000 Series
Category	Network Router
Language	English