Recipe 7.5 Creating a Default Route in EIGRP

7.5.1 Problem

You want to propagate a default route within EIGRP.

7.5.2 Solution

You can configure EIGRP to propagate a default route by simply redistributing a static route to 0.0.0.0/0, as follows:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip route 0.0.0.0 0.0.0.0 172.25.1.1
Router1(config)#access-list 7 permit 0.0.0.0
Router1(config)#router eigrp 55
Router1(config-router)#redistribute static                
Router1(config-router)#distribute-list 7 out static
Router1(config-router)#end
Router1#

7.5.3 Discussion

This example actually shows two things. We have redistributed a simple static default route into EIGRP, as shown in Recipe 7.3. And we have also implemented an outbound route filter that only affects the static routes, as discussed in Recipe 7.2. Note that because of the static keyword on the distribute-list command, this distribute list applies only to static routes. So, if there are many static routes on this router, this feature ensures that we will only redistribute the default route.

If we go to a downstream router, you can see that EIGRP is forwarding this route, and that it is accepted as a candidate default route:

Router2#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
  Known via "eigrp 55", distance 170, metric 2172416, candidate default path, type 
external
  Redistributing via eigrp 55
  Last update from 172.25.2.1 on Serial0.1, 00:02:16 ago
  Routing Descriptor Blocks:
  * 172.25.2.1, from 172.25.2.1, 00:02:16 ago, via Serial0.1
      Route metric is 2172416, traffic share count is 1
      Total delay is 20100 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
Router2#

You can look at the topology table to see how EIGRP classifies the default route:

Router2#show ip eigrp topology 0.0.0.0
IP-EIGRP (AS 55): Topology entry for 0.0.0.0/0
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
  Routing Descriptor Blocks:
  172.25.2.1 (Serial0.1), from 172.25.2.1, Send flag is 0x0
      Composite metric is (2172416/28160), Route is External
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 20100 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 172.25.25.1  
        AS number of route is 0
        External protocol is Static, external metric is 0
        Administrator tag is 0 (0x00000000)
        Exterior flag is set
Router2#

In this case, the command was issued on a downstream router that has received this default route via EIGRP. So it is shown as an external route. You can also see that the router 172.25.25.1 was responsible for introducing this external route into EIGRP, and that the external routing protocol is "static."

Recipe 7.10 shows another way of distributing a default gateway that doesn't mark the route as external.

7.5.4 See Also

Recipe 7.2; Recipe 7.3; Recipe 7.10