EIGRP - Enhanced Interior Gateway Routing Protocol

Master EIGRP for a successful Cisco certification journey

Originate Default-Route

We have multiple ways to originate a default route in EIGRP

    1. Using Network command
    2. Using Redistribute Static
    3. Default originate
    4. Summarization

Using Network Command

So this is the first way to originate a default route using network command, first we need a static default route in routing table as directly connected to any interface or we can use a static default route towards NULL0 interface then we can use Network 0.0.0.0 under Router EIGRP process to advertise it to EIGRP domain.

So here on Router R3 will be advertising a default route to EIGRP domain
    Add a static Default route on Router R3
    And then run redistribute static under Router EIGRP Process
        *R3(config)#ip route 0.0.0.0 0.0.0.0 NULL0
        *R3(config)#router eigrp 10
        *R3(config-router)#redistribute static
        *R3(config-router)#exit
    Now Router R3 Should advertise a default route to all EIGRP routers in this domain as External route
Let’s check on R1

So whenever we use Network command to originate a default route it advertises as an internal router.

Using Redistribute Static

As we have done in first example a default route originate using network commands, so here almost we will use same concept but this time we will originate default route using redistribution.
We need a static default route in routing table as directly connected to any interface or we can use a static default route towards NULL0 interface then we can use Redistribute connected under Router EIGRP process to advertise it to EIGRP domain.
Whenever we advertise default route using redistribution, routers install as external route with AS 170

As we can see here default route advertised by redistribution is installed in Routing Table as External route with AD 170

Using Summarization

So now we have one more mechanism to advertise a default route using Summarization, but this feature we use over the interface, When we use This feature over a interface to advertise a default route it basically suppress all the routes and just advertise a default route over the interface.

So now let’s use this topology to do summarization
Here we can see Router R1 is getting all the Specific routes from Router R3

So now on Router R3 interface we will do summarization using network 0.0.0.0 on interface f2/0
R3(config)#int fastEthernet 2/0
R3(config-if)#ip summary-address eigrp 10 0.0.0.0 0.0.0.0
Now we will check the output on R1 and will see the routes present in Routing Table

So this is how we can originate a default route using summarization also.