EIGRP Filtering with Prefix-list

Filtering using prefix-list. R6 loopback address is advertising to all the EIGRP routers.

We are going to block the R6 loopback address, This loopback address should be reachable only in LAN network (i.e) R1,R5 and R6.

R6 loopback is advertising R1 to all other downstream neighbor. Lets check the routing table on R4

R4#sh ip route 150.6.6.0

Routing entry for 150.6.6.0/24

  Known via "eigrp 100", distance 90, metric 2274816, type internal

  Redistributing via eigrp 100

  Last update from 155.1.14.1 on Serial0/0.41, 00:00:04 ago

  Routing Descriptor Blocks:

  * 155.1.14.1, from 155.1.14.1, 00:00:04 ago, via Serial0/0.41

      Route metric is 2274816, traffic share count is 1

      Total delay is 24100 microseconds, minimum bandwidth is 1544 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 2

So R4 getting the loopback address from R1 via s0/0.41.We can filter the address inbound or outbound. Here am going to use outbound filter because the loopback address should be used only in LAN network

R1#sh run

ip prefix-list LAN seq 5 deny 150.6.6.0/24

ip prefix-list LAN seq 10 permit 0.0.0.0/0 le 32

!

 ip authentication mode eigrp 100 md5

 ip authentication key-chain eigrp 100 CISCO

 no ip split-horizon eigrp 100

router eigrp 100

 network 150.1.0.0

 network 155.1.0.0

 distribute-list prefix LAN out Serial0/0.14

 no auto-summary

 neighbor 155.1.156.5 FastEthernet1/0

 neighbor 155.1.156.6 FastEthernet1/0

R4#sh ip route 150.6.6.0

Routing entry for 150.6.6.0/24

  Known via "eigrp 100", distance 90, metric 2274816, type internal

  Redistributing via eigrp 100

  Last update from 155.1.114.1 on Serial0/1, 00:01:03 ago

  Routing Descriptor Blocks:

  * 155.1.114.1, from 155.1.114.1, 00:01:03 ago, via Serial0/1

      Route metric is 2274816, traffic share count is 1

      Total delay is 24100 microseconds, minimum bandwidth is 1544 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 2

Note:

R4 not getting the 150.6.6.0 network via s0/0.41. But it can get the from R1 - R4 p2p link

After creating the prefix-list we have applied the prefix-list using distribute-list and in a outbound direction.