EIGRP Default route

8 min readNov 18, 2023

The default route is used by IP 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 an end location where there is only one exit path for any destination (internet).

We can also use the default routes for better network performance. How? For example, our routers on the access layer do not need to know all our routes in our Autonomous system. When we use a default route, we can significantly reduce the size of our router routing table and surely improve our network performance on the access layer.

Default routes help in reducing the size of your routing table. It’s the least preferred route in the routing table.

Let’s see the configuration:

Topology:

EIGRP DEFAULT ROUTE CONFIGURATION

TASK.

Configure the topology as per our diagram.
Assign IP address as per the topology.
configure EIGRP AS 100 and advertise interfaces.
We have two methods of advertising the default route

Default-network ****
Redistribution static

In this scenario, we use the redistribution static method
Configure static route on router 5 toward router 2
ensure router 5 able to ping all networks and all the routers are able to ping our 15. *** network

R1(config)#Interface fastethernet 0/0
R1(config-if)#Ip address 10.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#No keepalive
R1(config-if)#Exit

R1(config)#Interface serial 3/0
R1(config-if)#Ip address 1.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#Exit

R2(config)#Interface fastethernet 0/0

R2(config-if)#Ip address 20.1.1.1 255.0.0.0

R2(config-if)#No shutdown

R2(config-if)#No keepalive

R2(config-if)#Exit

R2(config)#Interface serial 3/0

R2(config-if)#Ip address 1.1.1.2 255.0.0.0

R2(config-if)#No shutdown

R2(config-if)#Exit

R2(config)#Interface serial 3/1

R2(config-if)#Ip address 4.4.4.2 255.0.0.0

R2(config-if)#No shutdown

R2(config-if)#Exit

R2(config)#Interface serial 3/2

R2(config-if)#Ip address 3.3.3.2 255.0.0.0

R2(config-if)#No shutdown

R2(config-if)#Exit

R2(config)#interface serial 3/3

R2(config-if)#ip address 5.5.5.2 255.0.0.0

R2(config-if)#no shutdown

R2(config-if)#exit

R3(config)#Interface fastethernet 0/0

R3(config-if)#Ip address 30.1.1.1 255.0.0.0

R3(config-if)#No shutdown

R3(config-if)#No keepalive

R3(config-if)#Exit

R3(config)#Interface serial 3/2

R3(config-if)#Ip address 3.3.3.1 255.0.0.0

R3(config-if)#No shutdown

R3(config-if)#Exit

R4(config)#Interface fastethernet 0/0

R4(config-if)#Ip address 40.1.1.1 255.0.0.0

R4(config-if)#No shutdown

R4(config-if)#No keepalive

R4(config-if)#Exit

R4(config)#Interface serial 3/1

R4(config-if)#Ip address 4.4.4.1 255.0.0.0

R4(config-if)#No shutdown

R4(config-if)#Exit

R5(config)#Interface fastethernet 0/0

R5(config-if)#Ip address 50.1.1.1 255.0.0.0

R5(config-if)#No shutdown

R5(config-if)#No keepalive

R5(config-if)#Exit

R5(config)#Interface serial 3/3

R5(config-if)#Ip address 5.5.5.1 255.0.0.0

R5(config-if)#No shutdown

R5(config-if)#Exit

R5(config)#Interface loopback 1

R5(config-if)#Ip address 15.0.1.1 255.255.255.0

R5(config-if)#Exit

R5(config)#Interface loopback 2

R5(config-if)#Ip address 15.0.2.1 255.255.255.0

R5(config-if)#Exit

R5(config)#Interface loopback 3

R5(config-if)#Ip address 15.0.3.1 255.255.255.0

R5(config-if)#Exit

R1#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 10.1.1.1 YES manual up up

Serial3/0 1.1.1.1 YES manual up up

R2#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 20.1.1.1 YES manual up up

Serial3/0 1.1.1.2 YES manual up up

Serial3/1 4.4.4.2 YES manual up up

Serial3/2 3.3.3.2 YES manual up up

Serial3/3 5.5.5.2 YES manual up up

R3#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 30.1.1.1 YES manual up up

Serial3/2 3.3.3.1 YES manual up up

R4#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 40.1.1.1 YES manual up up

Serial3/1 4.4.4.1 YES manual up up

R5#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 50.1.1.1 YES manual up up

Serial3/3 5.5.5.1 YES manual up down

Loopback1 15.0.1.1 YES manual up up

Loopback2 15.0.2.1 YES manual up up

Loopback3 15.0.3.1 YES manual up up

R1(config)#router eigrp 100

R1(config-router)#network 10.0.0.0

R1(config-router)#network 1.0.0.0

R1(config-router)#no auto-summary

R1(config-router)#exit

*Dec 4 05:15:11.879: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 1.1.1.2 (Serial3/0) is up: new adjacency

R2(config)#router eigrp 100

R2(config-router)#network 20.0.0.0

R2(config-router)#network 1.0.0.0

R2(config-router)#network 4.0.0.0

R2(config-router)#network 3.0.0.0

R2(config-router)#no auto-summary

R2(config-router)#exit

*Dec 4 05:16:09.051: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 3.3.3.1 (Serial3/2) is up: new adjacency

*Dec 4 05:15:11.975: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 1.1.1.1 (Serial3/0) is up: new adjacency

*Dec 4 05:16:44.895: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 4.4.4.1 (Serial3/1) is up: new adjacency

R2(config)#router eigrp 100

R2(config-router)#redistribute static

R2(config-router)#exit

R2(config)#ip route 0.0.0.0 0.0.0.0 5.5.5.1

R2(config)#end

R3(config)#router eigrp 100

R3(config-router)#network 30.0.0.0

R3(config-router)#network 3.0.0.0

R3(config-router)#no auto-summary

R3(config-router)#exit

*Dec 4 05:16:09.127: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 3.3.3.2 (Serial3/2) is up: new adjacency

R4(config)#router eigrp 100

R4(config-router)#network 40.0.0.0

R4(config-router)#network 4.0.0.0

R4(config-router)#no auto-summary

R4(config-router)#exit

R4(config)#end

*Dec 4 05:16:44.807: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 4.4.4.2 (Serial3/1) is up: new adjacency

R5(config)#ip route 4.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 3.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 20.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 30.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 40.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 10.0.0.0 255.0.0.0 5.5.5.2

R5(config)#ip route 1.0.0.0 255.0.0.0 5.5.5.2

R5(config)#end

R2#clear ip eigrp 100 neighbors

R1#show ip route eigrp

Codes: L — local, C — connected, S — static, R — RIP, M — mobile, B — BGP

D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area

N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2

E1 — OSPF external type 1, E2 — OSPF external type 2

i — IS-IS, su — IS-IS summary, L1 — IS-IS level-1, L2 — IS-IS level-2

ia — IS-IS inter area, * — candidate default, U — per-user static route

o — ODR, P — periodic downloaded static route, H — NHRP, l — LISP

+ — replicated route, % — next hop override

Gateway of last resort is 1.1.1.2 to network 0.0.0.0

D*EX 0.0.0.0/0 [170/2681856] via 1.1.1.2, 00:00:53, Serial3/0

D 3.0.0.0/8 [90/2681856] via 1.1.1.2, 00:00:53, Serial3/0

D 4.0.0.0/8 [90/2681856] via 1.1.1.2, 00:00:53, Serial3/0

D 20.0.0.0/8 [90/2172416] via 1.1.1.2, 00:00:53, Serial3/0

D 30.0.0.0/8 [90/2684416] via 1.1.1.2, 00:00:53, Serial3/0

D 40.0.0.0/8 [90/2684416] via 1.1.1.2, 00:00:53, Serial3/0

R2#show ip pro

*** IP Routing is NSF aware ***

Routing Protocol is “eigrp 100”

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

Redistributing: static

EIGRP-IPv4 Protocol for AS(100)

Metric weight K1=1, K2=0, K3=1, K4=0, K5=0

NSF-aware route hold timer is 240

Router-ID: 20.1.1.1

Topology : 0 (base)

Active Timer: 3 min

Distance: internal 90 external 170

Maximum path: 4

Maximum hopcount 100

Maximum metric variance 1

Automatic Summarization: disabled

Maximum path: 4

Routing for Networks:

1.0.0.0

3.0.0.0

4.0.0.0

20.0.0.0

Routing Information Sources:

Gateway Distance Last Update

1.1.1.1 90 00:01:45

3.3.3.1 90 00:01:45

4.4.4.1 90 00:01:45

Distance: internal 90 external 170

R3#show ip route eigrp

Codes: L — local, C — connected, S — static, R — RIP, M — mobile, B — BGP

D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area

N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2

E1 — OSPF external type 1, E2 — OSPF external type 2

i — IS-IS, su — IS-IS summary, L1 — IS-IS level-1, L2 — IS-IS level-2

ia — IS-IS inter area, * — candidate default, U — per-user static route

o — ODR, P — periodic downloaded static route, H — NHRP, l — LISP

+ — replicated route, % — next hop override

Gateway of last resort is 3.3.3.2 to network 0.0.0.0

D*EX 0.0.0.0/0 [170/2681856] via 3.3.3.2, 00:02:27, Serial3/2

D 1.0.0.0/8 [90/2681856] via 3.3.3.2, 00:02:27, Serial3/2

D 4.0.0.0/8 [90/2681856] via 3.3.3.2, 00:02:27, Serial3/2

D 10.0.0.0/8 [90/2684416] via 3.3.3.2, 00:02:24, Serial3/2

D 20.0.0.0/8 [90/2172416] via 3.3.3.2, 00:02:27, Serial3/2

D 40.0.0.0/8 [90/2684416] via 3.3.3.2, 00:02:27, Serial3/2

R4#show ip route eigrp

Codes: L — local, C — connected, S — static, R — RIP, M — mobile, B — BGP

D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area

N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2

E1 — OSPF external type 1, E2 — OSPF external type 2

i — IS-IS, su — IS-IS summary, L1 — IS-IS level-1, L2 — IS-IS level-2

ia — IS-IS inter area, * — candidate default, U — per-user static route

o — ODR, P — periodic downloaded static route, H — NHRP, l — LISP

+ — replicated route, % — next hop override

Gateway of last resort is 4.4.4.2 to network 0.0.0.0

D*EX 0.0.0.0/0 [170/2681856] via 4.4.4.2, 00:02:52, Serial3/1

D 1.0.0.0/8 [90/2681856] via 4.4.4.2, 00:02:52, Serial3/1

D 3.0.0.0/8 [90/2681856] via 4.4.4.2, 00:02:52, Serial3/1

D 10.0.0.0/8 [90/2684416] via 4.4.4.2, 00:02:49, Serial3/1

D 20.0.0.0/8 [90/2172416] via 4.4.4.2, 00:02:52, Serial3/1

D 30.0.0.0/8 [90/2684416] via 4.4.4.2, 00:02:52, Serial3/1

R5#show ip route

Codes: L — local, C — connected, S — static, R — RIP, M — mobile, B — BGP

D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area

N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2

E1 — OSPF external type 1, E2 — OSPF external type 2

i — IS-IS, su — IS-IS summary, L1 — IS-IS level-1, L2 — IS-IS level-2

ia — IS-IS inter area, * — candidate default, U — per-user static route

o — ODR, P — periodic downloaded static route, H — NHRP, l — LISP

+ — replicated route, % — next hop override

Gateway of last resort is not set

S 1.0.0.0/8 [1/0] via 5.5.5.2

S 3.0.0.0/8 [1/0] via 5.5.5.2

S 4.0.0.0/8 [1/0] via 5.5.5.2

5.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 5.0.0.0/8 is directly connected, Serial3/3

L 5.5.5.1/32 is directly connected, Serial3/3

S 10.0.0.0/8 [1/0] via 5.5.5.2

15.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

C 15.0.1.0/24 is directly connected, Loopback1

L 15.0.1.1/32 is directly connected, Loopback1

C 15.0.2.0/24 is directly connected, Loopback2

L 15.0.2.1/32 is directly connected, Loopback2

C 15.0.3.0/24 is directly connected, Loopback3

L 15.0.3.1/32 is directly connected, Loopback3

S 20.0.0.0/8 [1/0] via 5.5.5.2

S 30.0.0.0/8 [1/0] via 5.5.5.2

S 40.0.0.0/8 [1/0] via 5.5.5.2

50.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 50.0.0.0/8 is directly connected, FastEthernet0/0

L 50.1.1.1/32 is directly connected, FastEthernet0/0

R1#traceroute 50.1.1.1