EIGRP Static Neighbor

EIGRP by default uses multicast for neighbor discovery but it also allows you to configure EIGRP neighbors statically. Once you do this, EIGRP will only use unicast and disables EIGRP multicast on the selected interface.

This could be useful in certain scenarios where multicast is not supported or when you want to reduce the overhead of multicast traffic. Here’s an example:

EIGRP Frame Relay Multicast Replicated PVCs

Above we have a frame-relay hub and spoke network. The hub and spoke1 routers are the only two routers that are running EIGRP. When the hub router sends an EIGRP multicast packet, it will be replicated on all PVCs. All 4 spoke routers will receive this multicast traffic even though only spoke1 is interested in it.

In a scenario like this, it would make sense to configure the EIGRP neighbor statically so that multicast won’t be used.

Let’s see how we can configure EIGRP static neighbors…

Configuration

For this demonstration I’ll use the following two routers:

EIGRP Frame-relay two routers

R1 and R2 are connected through frame-relay. Here’s the configuration of the interfaces:

R1#show run | begin Serial0/0
interface Serial0/0
 ip address 192.168.12.1 255.255.255.0
 encapsulation frame-relay
 clock rate 2000000
 frame-relay map ip 192.168.12.2 102
 no frame-relay inverse-arp
R2#show run | begin Serial0/0 
interface Serial0/0
 ip address 192.168.12.2 255.255.255.0
 encapsulation frame-relay
 clock rate 2000000
 frame-relay map ip 192.168.12.1 201
 no frame-relay inverse-arp

Above you can see that frame-relay Inverse ARP has been disabled, two static frame-relay maps are used for our mappings. This means that we are unable to send any broadcast or multicast traffic through this PVC. You can also verify this with the following command:

R1#show frame-relay map
Serial0/0 (up): ip 192.168.12.2 dlci 102(0x66,0x1860), static,
              CISCO, status defined, active
R2#show frame-relay map 
Serial0/0 (up): ip 192.168.12.1 dlci 201(0xC9,0x3090), static,
              CISCO, status defined, active

As you can see the frame-relay mappings are there but the broadcast keyword is missing. Let’s configure EIGRP to use static neighbors:

R1(config)#router eigrp 12
R1(config-router)#network 192.168.12.0
R1(config-router)#neighbor 192.168.12.2 Serial 0/0 
R2(config)#router eigrp 12
R2(config-router)#network 192.168.12.0
R2(config-router)#neighbor 192.168.12.1 Serial 0/0

You only have to use the neighbor command to specify the remote neighbor and the interface to reach it. After a few seconds the neighbor adjacency will appear:

R1#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 12: Neighbor 192.168.12.2 (Serial0/0) is up: new adjacency
R2#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 12: Neighbor 192.168.12.1 (Serial0/0) is up: new adjacency

You you can also verify your static neighbors with the show ip eigrp neighbors command:

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Forum Replies

  1. Hi Andrew,

    First off, Thank you for extending your help!

    I want to accomplish this WITHOUT distributing or redistributing into EIGRP neighbors within the same AS. I actually tried your recommendation (below) last week in my lab, thinking it would work, but apparently it didn’t!

    R1(config)#router eigrp 1
    R1(config-router)#network 192.168.3.0 0.0.0.255
    R1(config-router)#network 192.168.5.0 0.0.0.255
    

    Here’s what R1 has in its RIB table as static:

    ip route 192.168.2.0 255.255.255.0 192.168.24.4
    ip route 192.168.3.0 255.255.255.0 192.168.24.4 (needs to be routed vi
    ... Continue reading in our forum

  2. CARL: where I added 6 static routes and wanted to advertise 192.168.3.x/24 192.168.5.x/24

    R4-Carl#sh ip route
    C    192.168.12.0/24 is directly connected, GigabitEthernet0/0
    D    192.168.13.0/24 [90/30720] via 192.168.12.1, 00:01:07, GigabitEthernet0/0
    C    192.168.24.0/24 is directly connected, GigabitEthernet0/1
    S    192.168.4.0/24 [1/0] via 192.168.24.4
    S    192.168.5.0/24 [1/0] via 192.168.24.4
    D    192.168.34.0/24 [90/30720] via 192.168.24.4, 00:01:07, GigabitEthernet0/1
    S    192.168.0.0/24 [1/0] via 192.168.24.4
    S    192.168.1.0/24 [1/0] via 192.168.24.4
    S
    ... Continue reading in our forum

  3. Hi Syed,
    I have an answer for you. Your detailed information was very helpful, so thanks for that. EIGRP does NOT advertise static routes (except if you tell it to do redistribution), unless it considers the route to be connected to a local interface. To understand this, you should know that static routes can be defined two different ways:

    1. The route can point to a next hop address, as you have done: ip route 192.168.4.0 255.255.255.0 192.168.24.4
    2. The route can point to an interface such as: ip route 192.168.4.0 255.255.255.0 serial0/0/0

    When you use an i

    ... Continue reading in our forum

  4. Hello Linda!

    When you add the EIGRP implementation, make sure you are configuring the static neighbour relationship correctly.

    The frame-relay map <em>protocol protocol_address</em> [broadcast] command forwards broadcasts to the specified address when multicast is not enabled. By using static neighbour relationships for EIGRP we are inherently using only unicast so this command would make no difference.

    Check your config again and if you still have problems, copy and paste the relevant parts of your config so we can take a look.

    I hope this was helpful!

    Laz

  5. Hello Hussein.

    When you set up a static neighbour on an EIGRP enabled interface of a router, the interface changes to using unicast EIGRP updates to the specific neighbour. This DISABLES multicast updates. You cannot have both unicast and multicast functioning on the same interface. They are mutually exclusive.

    I hope this has been helpful!

    Laz

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