EIGRP Route Filtering via Prefix-List Help Hello, I'm trying to understand why a prefix-list is not working the way I thought it should. I have a LAN Subnet, 200.50.5.0/27 that I want to be able to access the core network but I do not want the core to be able to access it. We then configure EIGRP with a distribute-list command that references the prefix list and is applied outbound: WEST#sh run begin router router eigrp 10 network 10.0.0.0 network 192.168.1.0 0.0.0.3 distribute-list prefix West-PF out no auto-summary To verify, the show ip protocols command is useful here. However, when the following distribute-list with prefix-list 'EIGRP-ROUTES' is applied only the subnet 3.3.3.3/32 is learned through the subinterface f0/0.3 and the physical interface f0/0. You can test with many forms, changing the permit/deny of prefix-lists and the application to the distribute-list command. Go to the configuration of the EIGRP process and use the distribute-list command to see your options. As you can see we can choose between an access-list, a prefix-list or a route-map. Let’s start with the access-list. You are probably familiar with the concept of access-lists if you studied CCNA. EIGRP: DEEP Dive into Prefix-List configurations, Access-list vs Prefix-list, using Prefix-Lists to Filter EIGRP routes with Distribute-Lists! Posted on May 10, 2017 October 2, 2019 by Loopy Only the NBMA and Ethernet segments will be used for quick demonstrations and clarity, unless R4 or R5 is needed for demonstration.
In our route redistribution with distribute-lists lab, we allowed some routes to be redistributed from RIP into OSPF while preventing the advertisement of other RIP networks. We also did a little RIP-only filtering, and now it’s EIGRP’s turn in the lab.
Distribute lists can also filter all routes from being advertised via a given interface without making that interface passive and losing the adjacency, as you’ll see in our next lab using the following topology. We’re not performing route redistribution in this particular lab; we’re only working with EIGRP.
R2 is advertising those two loopback networks into EIGRP. R1 sees them, as does R5.
We’d like to prevent R5 from seeing those routes while allowing R1 to have them. We could make the FastEthernet interface on R1 passive, but that means no Hellos leave that interface, which in turn means we’re gonna lose that adjacency. That’s not acceptable.
Eigrp Distribute-list Prefix Gateway
Let’s get the interface back to a non-passive state and consider other options.
We could write an ACL that denies all traffic and then apply it to R1 – or can we? Let’s find out!
The routes have been successfully filtered. R5 no longer has the routes, but it still has the adjacency to R1.
Eigrp Route Filtering Prefix List
If we ran into a situation where R1 received additional routes that we did want R5 to have, we’d need to go with a configuration similar to the previous lab, where we filtered some routes with a distribute-list.
You can verify your distribute list with show ip protocols. The pertinent output:
We can also use distribute-list to filter EIGRP routes when redistribution is involved, and we’ll do just that in our next lab, which I’ll post on August 4, 2018. Right now, check out my CCNP ROUTE Study Guide on Amazon along with these other redistribution tutorials.