Configuring EIGRP Default Route Propagation on Cisco Packet Tracer

Pre-requisite: EIGRP fundamentals, EIGRP Configuration.

With respect to EIGRP or any routing protocol, summarization is a significant tool to create a boundary for query propagation If a router receives a query for a network it does not have in its topology table, it’ll straightaway transmit a reply indicating an unreachable destination (Destination Host Unreachable), without itself going active and propagating the Query further.
Route summarization reduces the amount of routing information that routers must exchange, process, and maintain, which ultimately allows for faster topology convergence and less router load (CPU utilization) within the network. It also restricts the size of an area that is affected by network changes by hiding the changes in the individual networks behind a single advertised summary route.

Methods For Learning Default Routes in EIGRP :

Method	Description
Static route to 0.0.0.0 with the redistribute static command.	Redistributes/propagates the default static route within the EIGRP routing domain
Using manual summarization with the IP default-network command.	EIGRP Formerly supported the use of this command. But as this command uses the candidate default flag which the EIGRP no longer supports in recent IOS versions, it is best to not use this command altogether.
Using summary routes with the ip summary-address eigrp <autonomous-system> <address netmask> command on a per-interface basis.	Manual summarization is configured on a per-interface basis for a specific EIGRP autonomous system.

Configuring EIGRP Default Route Propagation:

Step 1: Create the 2 router topology in Cisco Packet Tracer as shown in the image below :

Step 2: Configure the IPv4 address on the physical interface on the routers :

R1(config)#hostname R1
R1(config)#interface FastEthernet0/0
R1(config-if)#ip address 10.0.0.1 255.255.255.0
R1(config-if)#no shutdown

R2(config)#hostname R2
R2(config)#interface FastEthernet0/0
R2(config-if)#ip address 10.0.0.2 255.255.255.0
R2(config-if)#no shutdown

Step 3: Configure a loopback interface on R1 with an IPv4 address :

R2(config)#interface Loopback0
R2(config-if)#ip address 1.1.1.1 255.255.255.255

Step 4: Configure a loopback interface on R2 with an IPv4 address :

R2(config)#interface Loopback0
R2(config-if)#ip address 2.2.2.2 255.255.255.255

Step 5: Configuring the EIGRP process on both routers with the command router eigrp <1-65535 Autonomous system number> :

R1(config)#router eigrp 1
R1(config-router)#network 10.0.0.0
R1(config-router)#network 1.1.1.1

R2(config)#router eigrp 1
R2(config-router)#network 10.0.0.0
R2(config-router)#network 2.2.2.2

Step 6: Checking the IPv4 routing table on the routers and see the EIGRP route entry :

• No default route entry in the routing table.

R1#show ip route

R2#show ip route

Step 7:  Configuring R1 to always originate and propagate a default route throughout the entire EIGRP autonomous system :

R1(config)#int gig0/0
R1(config-if)#ip summary-address
 eigrp 1 0.0.0.0 0.0.0.0

• Whenever a summary route is advertised, the router performing the summarization automatically installs a discard route for this summary route into its routing table.
• The network and netmask in this discard route are identical to the network and netmask of the advertised summary, and the outgoing interface is set to Null0.
• To verify this, check the IPv4 routing table of R1 and see the entry :

R1#show ip route 

Step 8: Verifying whether the default route is being propagated correctly by R1 or not by viewing the routing table on R2 :

R2#show ip route

Step 9: Checking connectivity throughout the topology :

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