EIGRP Default Network Route

In this lesson we’ll take a look how we can configure a default route in EIGRP.  Basically there are two methods how you can do this:

• Create a static route and advertise it into EIGRP.
• Flag an EIGRP route as the default network.

We will take a look at both methods. This is the topology we will use:

R1 and R2 are configured for EIGRP, R2 is connected to an ISP router. Behind the ISP is network 3.3.3.0 /24 that we can use to test our default route.

Configuration

Here’s the configuration of R1 and R2:

R1#show run | section eigrp
router eigrp 12
 network 192.168.12.0
 no auto-summary

R2#show run | section eigrp
router eigrp 12
 network 192.168.12.0
 no auto-summary

Nothing special, R1 and R2 are neighbors but that’s it.

Static Default Route

Let’s start with the first option, the static default route:

R2(config)#ip route 0.0.0.0 0.0.0.0 FastEthernet 0/1

R2(config)#router eigrp 12
R2(config-router)#network 0.0.0.0

We configure the default route on R2 with FastEthernet 0/1 as the exit interface. In EIGRP we can use the network 0.0.0.0 command to advertise this. This might sound strange but it works, normally you can only use the network command to advertise networks on interfaces but EIGRP wil make an exception for this default route.

Let’s see what R1 thinks of this:

R1#show ip route eigrp | begin 0.0.0.0
Gateway of last resort is 192.168.12.2 to network 0.0.0.0

D*    0.0.0.0/0 [90/30720] via 192.168.12.2, 00:01:11, FastEthernet0/0

R1 has learned the default route.

hostname ISP
!
interface FastEthernet0/0
 ip address 192.168.23.3 255.255.255.0
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.0
!
ip route 192.168.12.0 255.255.255.0 192.168.23.2
!
end

hostname R1
!
interface FastEthernet0/0
 ip address 192.168.12.1 255.255.255.0
!
router eigrp 12
 no auto-summary
 network 192.168.12.0
!
end

hostname R2
!
interface FastEthernet0/1
 ip address 192.168.23.2 255.255.255.0
!
interface FastEthernet1/0
 ip address 192.168.12.2 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 FastEthernet0/1
!
router eigrp 12
 no auto-summary
 network 192.168.12.0
 network 0.0.0.0
!
end

R2(config)#router eigrp 12
R2(config-router)#no network 0.0.0.0          

R2(config)#no ip route 0.0.0.0 0.0.0.0 FastEthernet 0/1

There we go…let’s continue!

IP Default Network

This one is a bit tricky, we can use the ip default-network command to tell other EIGRP routers that this is a network of “last resort”. This means that they can use it as a default route. We will advertise the network between R2 and ISP in EIGRP and configure it as the “default network”: