EIGRP Offset-List

R4#sh ip route | sec 150.5

     150.5.0.0/24 is subnetted, 1 subnets

D       150.5.5.0 [90/2300416] via 155.1.114.1, 00:01:35, Serial0/1

                           [90/2300416] via 155.1.14.1, 00:01:35, Serial0/0.41

R4 learning the R5's Loopback address via s0/1 and s0/0.41. Now we are going to add the offset(Metric) on s0/1. To make the s0/1 as backup path in case the s0/0.41 FR in down the backup path s0/1 will be used to forward packets

R4#traceroute 150.5.5.5

Type escape sequence to abort.

Tracing the route to 150.5.5.5

  1 155.1.114.1 116 msec

    155.1.14.1 72 msec

    155.1.114.1 8 msec

See we are using both the link R4's s0/1 and s0/0.41. To create s0/1 as a backup path we will add a metric of 36 on s0/1.

R4#sh run

access-list 1 permit 150.5.5.0 0.0.0.255

!

 ip authentication mode eigrp 100 md5

 ip authentication key-chain eigrp 100 CISCO

router eigrp 100

 offset-list 1 in 34 Serial0/1

 network 150.4.0.0

 network 155.1.0.0

 no auto-summary

R4#sh ip route | sec 150.5

     150.5.0.0/24 is subnetted, 1 subnets

D       150.5.5.0 [90/2300416] via 155.1.14.1, 00:02:26, Serial0/0.41

R4#traceroute 150.5.5.5

Type escape sequence to abort.

Tracing the route to 150.5.5.5

  1 155.1.14.1 180 msec 156 msec 8 msec

  2 155.1.156.5 220 msec *  88 msec

And at last we have made the R4 S0/1 as backup path. Lets shutdown the interface s0/0.41 and check whether it uses the backup path or not.

R4(config)#int s0/0.41

R4(config-subif)#sh

R4#traceroute 150.5.5.5

Type escape sequence to abort.

Tracing the route to 150.5.5.5

  1 155.1.114.1 144 msec 52 msec 96 msec

  2 155.1.156.5 172 msec *  116 msec