Configuring EIGRP Maximum Paths in Cisco

Pre-requisite: EIGRP Configuration, EIGRP Implementation in Cisco.

EIGRP is a CISCO proprietary protocol for routing. EIGRP calculates the best route to a destination using the metric value it is based on.

1. Link bandwidth
2. Delay

EIGRP selects the shortest path and installs that path in the routing table. If there are multiple paths to the destination with the same administrative distance and a metric value, all the routes are installed in the routing table.

In Equal-cost load balancing, if a router has two or more paths to a destination with equal cost metrics, then the router forwards the packets using all the paths equally. However, the protocol should have an equal administrative distance to the destination when forwarding packets, and in our case the protocol is EIGRP. Using load balancing, the router uses network segments and bandwidth more efficiently.

Cisco IOS Software can balance the load across up to four equal-cost paths by default. We can configure the EIGRP load balancing up to 16 equal-cost paths and a maximum of 32 equal-cost routes in the routing table. The subcommand “maximum-path” in the router configuration mode is used to configure EIGRP maximum paths.

Syntax: 

ROUTER(config-router)#maximum-paths <1-32>

Configuring EIGRP Maximum Paths :

Step 1: Create a physical topology in GNS3 as shown in the image below :

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

On R1 :

R1(config)#interface FastEthernet0/0
R1(config-if)#ip address 12.1.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#interface FastEthernet1/0
R1(config-if)#ip address 13.1.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#interface FastEthernet1/1
R1(config-if)#ip address 14.1.1.1 255.255.255.0
R1(config-if)#no shutdown

On R2 :

R2(config)#interface FastEthernet0/0
R2(config-if)#ip address 12.1.1.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#interface FastEthernet1/0
R2(config-if)#ip address 10.1.1.2 255.255.255.0
R2(config-if)#no shutdown

On R3 :

R3(config)#interface FastEthernet0/0
R3(config-if)#ip address 13.1.1.2 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#interface FastEthernet1/0
R3(config-if)#ip address 10.1.1.3 255.255.255.0
R3(config-if)#no shutdown

On R4 :

R4(config)#interface FastEthernet0/0
R4(config-if)#ip address 14.1.1.2 255.255.255.0
R4(config-if)#no shutdown
R4(config-if)#interface FastEthernet1/0
R4(config-if)#ip address 10.1.1.4 255.255.255.0
R4(config-if)#no shutdown

ON SERVER :

SERVER(config)#interface FastEthernet0/0
SERVER(config-if)ip address 10.1.1.1 255.255.255.0
SERVER(config-if)#no shutdown

Step 3: 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 0.0.0.0
R1(config-router)#no auto-summary

R2(config)#router eigrp 1
R2(config-router)#network 0.0.0.0
R2(config-router)#no auto-summary

R3(config)#router eigrp 1
R3(config-router)#network 0.0.0.0
R3(config-router)#no auto-summary

R4(config)#router eigrp 1
R4(config-router)#network 0.0.0.0
R4(config-router)#no auto-summary

SERVER(config)#router eigrp 1
SERVER(config-router)#network 0.0.0.0
SERVER(config-router)#no auto-summary

Step 4: Check the IPv4 routing table on the routers and see the EIGRP route entries :

R1#show ip route

• There are 3 equal cost routes to the network 10.1.1.0/24

R2#show ip route

R3#show ip route

R4#show ip route

SERVER#show ip route

Step 5: Configure R1 to use no more than 1 path to get to any given destination, with router eigrp subcommand maximum-paths <1-16> :

R1(config)#router eigrp 1
R1(config-router)#maximum-paths 1
R1(config-router)#end

Step 6: Check the IPv4 routing table of R1 again to verify the changes in the maximum-paths:

R1#show ip route

• There is only 1 EGIRP route to the network 10.1.1.0 /24 after configuring maximum paths to 1.

Check Connectivity : 

  ping 12.1.1.2
  ping 13.1.1.2
  ping 14.1.1.2
  ping 10.1.1.0

  ping 13.1.1.0
  ping 14.1.1.0
  ping 10.1.1.0

  ping 12.1.1.0
  ping 13.1.1.0
  ping 14.1.1.0
  ping 10.1.1.0

  ping 12.1.1.0
  ping 13.1.1.0
  ping 14.1.1.0
  ping 10.1.1.0

  ping 10.1.1.0
  ping 12.1.1.0
  ping 13.1.1.0
  ping 14.1.1.0