Last Updated on July 31, 2021 by Admin 1
You are configuring EIGRP on a spoke router in a hub-and-spoke topology. In an effort to keep the routing table small, the hub router has been configured to send only a default route to the remote routers.
What command would you use on the spoke routers to enable them to send only connected and summary routes to the hub router, and prevent the hub router from sending a query to the spoke router when a route is lost elsewhere?
- eigrp stub
- eigrp stub static
- eigrp passive
- eigrp stub receive-only
The eigrp stub command is used to configure a router to send only connected and summary routes to its neighboring router. For example, examine the following output of the show ip route command that was executed on a router configured as a stub router:
router10#show ip route C 172.16.5.0/24 is directly connected, Serial 0 D 192.168.7.0/24 [90/16523564] via 172.16.4.1, 00:21:20, Serial 1 D 172.16.0.0/16 is a summary, 00:21:23, Null 0 C 172.16.4.0/24 is directly connected, Serial 2
The routes that will be advertised are 172.16.5.0/24, 172.16.4.0/24, and the summary route 172.16.0.0/16. The first two is directly connected routes, and the last is the summary route that is auto configured by the EIGRP process.
When the stub feature is enabled on a router, the router will announce itself as a stub router. Neighbor routers will not query a stub router for alternate routes when a route is lost elsewhere in the network. The EIGRP stub feature works well in hub-and-spoke topologies when the goal is to minimize the amount of EIGRP bandwidth and processing associated with the spoke router. The eigrp stub command has the following syntax:
eigrp stub [receive-only | connected | static | summary]
When you do not specify any keywords with the command, connected and summary are used by default.
receive-only: Prevents the router from sending any connected or summary routes.
connected: Instructs the router to send connected routes.
static: Instructs the router to send static routes that were redistributed by using the redistribute static command.
summary: Instructs the router to send summary routes.
These parameters can be combined to resolve various problems, as seen in the following image:
Router A is not receiving the route to the 172.16.1.0/16 network because Router B, which stands between Router A and C, is configured with the eigrp stub-receive-only command. This is resulting in hosts from the corporate office being unable to connect to hosts in the 172.16.0.0/16 network. If there were a legitimate reason to keep Router B configured with the eigrp stub-receive-only command, the problem could be solved by executing the following command set on Router A:
routerA(config)# router eigrp 20 routerA(config-router)# ip summary-address eigrp 20 172.16.0.0 255.255.0.0 routerA(config-router)# eigrp stub connected summary
This command set would create a summary address for the 172.16.0.0/16 network and then advertise it to the corporate office as a result of using the eigrp stub connected summary command. The inclusion of the connected parameter ensures that the directly connected networks will also be advertised, to ensure that hosts in the corporate office can reach the 172.16.0.0/16 network.
The eigrp stub static command instructs the router to send static routes that were redistributed by using the redistribute static command. Examine the EIGRP configuration shown below:
ip route 10.4.4.0 255.255.255.0 10.4.3.10
Route eigrp 200
Redistribute static 1000 1 255 1 1500
Network 10.4.1.0 0.0.0.3.
Network 10.4.2.0 0.0.0.255
Eigrp stub static
With this configuration, the router would not advertise any of the networks defined in the network statements, but would only advertise the static route configured with the line ip route 10.4.4.0 255.255.255.0 10.4.3.10.
Eigrp passive is not a valid Cisco command.
Eigrp stub receive-only will cause the router to not advertise any routes. The router will only receive updates.
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Configure and verify EIGRP stubs