Configuration of Default Routes in EIGRP

Configuration of Default Routes in EIGRP

In this post you will find the method on how to Configuration of Default Routes in EIGRP. One method to configure a default route within the EIGRP routing domain is by using the redistribute static command . You will find EIGRP Verification commands to include this static route in EIGRP updates to other routers.

Configuration of Default Static Routes in EIGRP

The use of a static route at 0.0.0.0/0 as the default route does not constitute protocol dependent routing. The default static route " quad zero " can be used with any routing protocol currently supported. In general, the default static route is configured on the router that has a connection to a network outside the EIGRP routing domain; for example, to an ISP. In below image, R2 is the gateway router that connects the EIGRP routing domain to the Internet.

When the default static route is configured, it is necessary to propagate that route throughout the EIGRP domain, as shown in Image 2.

One method to propagate a default static route within the EIGRP routing domain is by using the redistribute static command . This command tells EIGRP to include static routes in its EIGRP updates to other routers.
The default static route configuration and the redistribute static command on router R2 are shown below.

R2 (config) # ip route 0.0.0.0 0.0.0.0 serial 0/1/0 
R2 (config) # router eigrp 1 
R2 (config-router) # redistribute static

Now, it is verified that router R2 received the default route and installed it in its IPv4 routing table.

R2 # show ip route | include 0.0.0.0
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S * 0.0.0.0/0 is directly connected, Serial0 / 1/0 
R2 #

In image below, the show ip protocols command verifies that R2 redistributes static routes within the EIGRP routing domain.

Verification of Default Routes Configurations in EIGRP

In the illustration, a part of the IPv4 routing tables of R1 and R3 is shown.

In the routing tables of R1 and R3, observe the routing origin and administrative distance of the new default route that was discovered using EIGRP. The default route entry that was discovered by EIGRP is identified by the following:

• D : This route was discovered in an EIGRP routing update.
• * : The route is a candidate for a default route.
• EX : The route is an external EIGRP route, in this case, a static route outside the EIGRP routing domain.
• 170 : administrative distance of an external EIGRP route.

Note that R1 selects R3 as the successor to the default route, because it has a smaller feasible distance. Default routes provide a default route to exit the routing domain and, like summary routes, minimize the number of entries in the routing table.

EIGRP FOR IPV6: DEFAULT ROUTE

Remember that EIGRP maintains independent tables for IPv4 and IPv6, therefore, a default IPv6 route must be propagated separately, as shown in Image 5.

Similar to what happens in EIGRP for IPv4, a default static route is configured on the gateway router (R2), as shown in Figure:

R2 (config) # ipv6 route :: / 0 serial 0/1/0 
R2 (config) # ipv6 router eigrp 2 
R2 (config-rtr) # redistribute static

The prefix :: / 0 and the prefix length are equivalent to the address and subnet mask 0.0.0.0 0.0.0.0 used in IPv4. Both are addresses composed entirely of zeros and with a prefix length / 0. The default static IPv6 route is redistributed in the EIGRP domain for IPv6 using the same static redistribute command that was used in EIGRP for IPv4.
Note : Some Cisco IOS may require that the redistribute static command include the EIGRP metric parameters so that the static route can be redistributed.

Verification of IPv6 Default Routes in EIGRP

Finally, the propagation of the IPv6 default static route can be verified by reviewing the Rv IPv6 routing table with the show ipv6 route command , as shown in Image 6.

Note that the successor or address of the next hop is not R2, but R3. This is because R3 provides a better route to R2, with a lower metric cost than R1.