Injecting (propagating) Default Route via EIGRP

Default Route: A route that matches the destination of all packets that are not matched by any other route in the IP routing table. It can also be called as the ultimate summary route 0.0.0.0/0 (all IPv4 addresses).

There are different methods to inject default route into EIGRP process:

  1.       Injecting static default route using redistribute command in EIGRP routing process or advertise the static default route.
  2.       Injecting static default route using default-network command.
  3.       Summarized the static default route (0.0.0.0/0)

In all these scenarios one must define the static default route first then you could advertise itredistribute it or create summary-address or make that static route as a default network.

To illustrate these methods I have set up a very simple topology.

image001

All these routers are routing the routes using EIGRP AS 100 except the network 30.1.1.0. This 30.1.1.0 network is emulating a remote network to which R1 and R2 are trying to reach. Hence the task of this lab is to inject default route into R1 and R2 so they can reach network 30.1.1.0.

Let’s check the routing table of each router.

R1:

Gateway of last resort is not set 

       1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

     2.0.0.0/24 is subnetted, 1 subnets

D       2.1.1.0 [90/307200] via 1.1.1.2, 00:13:47, FastEthernet0/0

     20.0.0.0/24 is subnetted, 1 subnets


D     20.1.1.0 [90/409600] via 1.1.1.2, 00:13:47, FastEthernet0/0

     10.0.0.0/24 is subnetted, 1 subnets

C       10.1.1.0 is directly connected, Loopback0

R2:Both the routers doesn’t contain 30.0.0.0 network. This is simply because R3 is not advertising it. So both the routers can’t reach it.

Gateway of last resort is not set 

     1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

     2.0.0.0/24 is subnetted, 1 subnets

C       2.1.1.0 is directly connected, FastEthernet0/1

     20.0.0.0/24 is subnetted, 1 subnets

C       20.1.1.0 is directly connected, Loopback0

     10.0.0.0/24 is subnetted, 1 subnets

D       10.1.1.0 [90/409600] via 1.1.1.1, 00:15:14, FastEthernet0/0

Redistributing Static Default route:

Let’s first try with injecting default route using redistribute command under EIGRP process. So, first we need
to define a static route on R2. Why R2 because it is directly connected to R3.

R2#config t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#ip route 0.0.0.0 0.0.0.0 f0/1 (0.0.0.0 means any route that is currently not in the routing table & will be forwarded to f0/1 interface)

R2(config)#router eigrp 100

R2(config-router)#redistribute static metric 1544 10 255 1 1500   

Now let’s check the routing table of R1:

Gateway of last resort is 1.1.1.2 to network 0.0.0.0 

     1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

     2.0.0.0/24 is subnetted, 1 subnets

D       2.1.1.0 [90/307200] via 1.1.1.2, 00:28:59,FastEthernet0/0

     20.0.0.0/24 is subnetted, 1 subnets

D       20.1.1.0 [90/409600] via 1.1.1.2, 00:28:59,FastEthernet0/0

     10.0.0.0/24 is subnetted, 1 subnets

C       10.1.1.0 is directly connected, Loopback0

D*EX 0.0.0.0/0 [170/1686016] via 1.1.1.2, 00:00:06, FastEthernet0/0

As you can see the default route has been successfully redistributed into R1.  D*EX means this route is a candidate default and it is redistributed via 1.1.1.2. Gateway of last resort is also the same interface for unknown network (0.0.0.0). Let’s try to ping 30.0.0.0 network from R1.

R1#ping 30.1.1.1

Type escape sequence to abort. 

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 24/44/68 ms

Once could also configure more specific static route if the network is known clearly. Like in our example we have clear information about the destination network right? (30.1.1.0) So we can configure static route as:
ip route 30.1.1.0 255.255.255.0 f0/1
However, the caveat is this wouldn’t be a candidate default route! Let’s test configuration and check the routing table on R1.

R2#config

Configuring from terminal, memory, or network [terminal]? t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#no ip route 0.0.0.0 0.0.0.0 FastEthernet0/1

R2(config)#ip route 30.1.1.0 255.255.255.0 f0/1

R2(config)#

R1#sh ip route

Gateway of last resort is not set 

     1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

     2.0.0.0/24 is subnetted, 1 subnets

D       2.1.1.0 [90/307200] via 1.1.1.2, 00:12:49, FastEthernet0/0

     20.0.0.0/24 is subnetted, 1 subnets

D       20.1.1.0 [90/409600] via 1.1.1.2, 00:12:54, FastEthernet0/0

     10.0.0.0/24 is subnetted, 2 subnets

C       10.41.41.0 is directly connected, Serial0/0

C       10.1.1.0 is directly connected, Loopback0

     30.0.0.0/24 is subnetted, 1 subnets

D EX    30.1.1.0 [170/1686016] via 1.1.1.2, 00:05:16, FastEthernet0/0 

If you carefully analyze the routing table then you would observe that the route is no more candidate default it is just an external route and gateway of last resort is also not set. Because * is not there in between D EX. * means candidate default. Let’s try to ping this network.

R1#ping 30.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max =24/53/84 ms

Good! We are able to get there, the only concern is, it is not a candidate default. 

Advertising Static Default route:

Now let’s play with one more variation. In this we will use the same static route but instead of redistributing it we will advertise this into EIGRP process. We will use static route of all zeros 0.0.0.0/0 and advertise it. And when we advertise the static route it will be internal EIGRP route to the neighbor router. 

R2#config t

R2(config)#no ip route 30.1.1.0 255.255.255.0 f0/1

R2(config)#ip route 0.0.0.0 0.0.0.0 f0/1

R2(config)#router eigrp 100

R2(config-router)#no redistribute static metric 1544 10 255 1 1500

R2(config-router)#network 0.0.0.0

Let’s check the routing table of R1

Gateway of last resort is 1.1.1.2 to network 0.0.0.0

      1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

     2.0.0.0/24 is subnetted, 1 subnets

D       2.1.1.0 [90/307200] via 1.1.1.2, 00:34:47, FastEthernet0/0

     20.0.0.0/24 is subnetted, 1 subnets

D       20.1.1.0 [90/409600] via 1.1.1.2, 00:34:52, FastEthernet0/0

     10.0.0.0/24 is subnetted, 2 subnets

C       10.41.41.0 is directly connected, Serial0/0

C       10.1.1.0 is directly connected, Loopback0

D*   0.0.0.0/0 [90/307200] via 1.1.1.2, 00:01:43, FastEthernet0/0

As you can see we have successfully advertised the default route here. Here is the route is indicated as D this means this is a normal EIGRP route and it is a candidate default. Similarly, one could also use the following method:

R2(config)#ip route 30.1.1.0 255.255.255.0 f0/1

R2(config)#router eigrp 100

R2(router)#network 30.0.0.0

The second method will not create candidate default!

Summarizing the Static Default
route:

We will use the same default route (0.0.0.0/0)

Configuration snapped:

R2(config)#ip route 0.0.0.0 0.0.0.0 f0/1

R2(config)#interface f0/0

R2(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0

Alright, now let’s try with Default-Network command and track how it goes.  

With the default-network command we can advertise a non-zero network number as the default network. To do so following two conditions must be always TRUE:

  1. The network number must be a class full network number (Class A, B or C).
  2. And the network must be in the routing table of the originating router.

Keeping these two conditions in mind we have to change the IP addressing scheme in our topology.

Notice: The network between R2 and R3 is change to class A. And IP addresses on both the interfaces have changed accordingly. I have also added one more router, R4 to see how the default network propagates in the network.

Since R2 is originating the default-network it should have this route in its routing table right? Let’s go and check it:

R2#sh ip route

Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

C    2.0.0.0/8 is directly connected, FastEthernet0/1

     20.0.0.0/24 is subnetted, 1 subnets

C       20.1.1.0 is directly connected, Loopback0

     10.0.0.0/24 is subnetted, 2 subnets

D       10.41.41.0 [90/2195456] via 1.1.1.1, 00:30:47, FastEthernet0/0

D       10.1.1.0 [90/409600] via 1.1.1.1, 00:30:47, FastEthernet0/0

     30.0.0.0/24 is subnetted, 1 subnets

R2 does have the network: C 2.0.0.0/8 is directly connected, FastEthernet0/1

Alright so both the conditions are TRUE so we are all set to go!

Again we need to define one static route to 30.1.1.0 network via
2.1.1.2 on R3

Ip route 30.1.1.0 255.255.255.0 2.1.1.2

Now let’s define the default network:

Ip default-network 2.0.0.0

Configuration snapped:

R2#config t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#ip route 30.1.1.0 255.255.255.0 2.1.1.2

R2(config)#ip default-network 2.0.0.0

R2(config)#end

 

Let’s check its routing table.

R2#sh ip routeAs you can see we have candidate default (C*) and static routes (S) both.

Gateway of last resort is not set 

     1.0.0.0/24 is subnetted, 1 subnets

C       1.1.1.0 is directly connected, FastEthernet0/0

C*   2.0.0.0/8 is directly connected, FastEthernet0/1

     20.0.0.0/24 is subnetted, 1 subnets

C       20.1.1.0 is directly connected, Loopback0

     10.0.0.0/24 is subnetted, 2 subnets

D       10.41.41.0 [90/2195456] via 1.1.1.1, 00:38:27,FastEthernet0/0

D       10.1.1.0 [90/409600] via 1.1.1.1, 00:38:27,FastEthernet0/0

     30.0.0.0/24 is subnetted, 1 subnets

S       30.1.1.0 [1/0] via 2.1.1.2

R2#

Let’s ping the remote network address 30.1.1.1

R2#ping 30.1.1.1 

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max =
28/35/48 ms

R2#

Let’s check the routing table of R4:

R4#sh ip route

Gateway of last resort is 10.41.41.1 to network 2.0.0.0

 

      1.0.0.0/24 is subnetted, 1 subnetsSure enough, we do have the candidate default (D*) via EIGRP and we are able to ping the remote network as well. And this method is effective for advertising connection to the Internet.

D       1.1.1.0 [90/2195456] via 10.41.41.1, 05:34:00, Serial0/0

D*   2.0.0.0/8 [90/2221056] via 10.41.41.1, 00:04:19, Serial0/0

     20.0.0.0/24 is subnetted, 1 subnets

D       20.1.1.0 [90/2323456] via 10.41.41.1, 02:28:07, Serial0/0

     10.0.0.0/24 is subnetted, 2 subnets

C       10.41.41.0 is directly connected, Serial0/0

D       10.1.1.0 [90/2297856] via 10.41.41.1, 05:34:00, Serial0/0

R4#ping 30.1.1.1 

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max =60/65/68 ms

R4#

 

 

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