Default route injection is a critical technique for
directing traffic to a gateway of last resort, commonly used in hub-and-spoke
topologies, internet breakouts, and redundant network designs. The specific
method you use will depend on the routing protocol.
The default route is used to forward any packet with a
destination not found in the routing table, which is why it is also called a
gateway of last resort. Also can be used at the end location where there is
only one exit path for any destination (internet).
Default routes help in reducing the size of your routing
table. It’s the last preferred route in the routing table
There are many ways to inject a default route in EIGRP. In this lab, we test four ways of injecting a default route.
The first method to inject a default route into EIGRP is to configure a static default route pointing to Null0, and then redistribute the default route into EIGRP when redistributing a static, connected, or EIGRP route for another autonomous system; the metric does not need to be assigned. The default route will be an external EIGRP route.
The second method for injecting a default route into EIGRP is to configure a network command with 0.0.0.0. You must have the static default route configured; otherwise, with the network 0.0.0.0, all the existing and future directly connected interfaces will be advertised in the AS. The default route will be an internal EIGRP route.
The third method for injecting a default route into EIGRP is to configure the IP summary-address EIGRP interface configuration command. With this command, you are summarizing all the class A, B, and C networks. This means that you are suppressing every route in your routing table, but if you must advertise a specific network, you must leak it. The default route will be an internal EIGRP route.
The fourth method of injecting a default route is to use IP default-network command.
The goal is to perform all the route injection methods in our topology.
- Configure the topology as per the diagram
- Configure IP addresses as per the topology
- Configure IGP EIGRP AS 65100.
- Advertise directly connected routes
- Configure the first method of route injection (redistribute default route static Null0)
- Configure the Second method of route injection (static and network 0.0.0.0)
- Configure the third method of route injection (only summary address)
- Configure the fourth method of route injection ( IP default-network)