We help IT Professionals succeed at work.

Remove a router from EIGRP AS

If I remove routers how do I identify which network statements and associated vlan interfaces to remove or modify?

The routers are connected to a layer 3 switch on layer 2 access ports and the vlan interfaces have either a /30 or a /24 suubnet mask.

I matched up the vlan interface with the ip address of the routers to be removed but I am not sure the best way to remove the network statements under the EIGRP process. Is this a manual process of looking at the config or can I run a command that will help identify which network statements to remove or modify?
Comment
Watch Question

Top Expert 2011
Commented:
You have to look at your configs and decide, there is no special command for this.
Commented:
That's the beauty of a link-state routing protocol like EIGRP:  You don't have to modify a thing!  If you remove the routers, EIGRP will take care that all the networks that were advertised by the routers are also removed from the routing tables of the remaining routers.  And you don't have to change one line of config (in theory, at least).

However, in practise, you would like to do some clean-up in the remaining routers, to prevent unauthorised devices using the now-vacant IP's to form adjacencies.  How that clean-up happens, depends how EIGRP was configured initially:  A common practise is that all point-to-point links between routers are assigned addresses out of a particular range, which then only require a single network statement in EIGRP to cover all the links to other routers.  When you remove routers, you can't remove that single statement, as you might break adjacencies to other routers that should remain.

What I will suggest, is that you remove all VLANs that connected to the removed routers that have a /30 mask.  You'll have to investigate what the /24 subnets are used for, as that can have other devices (that might not be routers) conneted on the VLANs.  For such VLANs, you might not be able to remove the neighbor statement, as it also tells the router what networks to advertise to other neighors.

To conclude:  Removing routers also require something no machine will do for you - design.  If you have a propper routing design (how routing should work), you should know what interfaces and network statements are required for neighbor adjacency, and what for network advertisement.  With this in place, it should be easy to spot what must remain, and what can be removed.
Hi,

You need to look at the network statements and see which interfaces match the network statements.

You can use

show ip protocols
show ip eigrp interfaces
show ip eigrp neighbors

to help identify eigrp peers and routing sources
Marius GunnerudSenior Systems Engineer
Top Expert 2013
Commented:
As mentioned above, you can remove a router from the network and EIGRP will reconverge and the routes will be updated on the other routers.

If you are just removing certain routes from a give router then you can use the following command to see which networks are configured to be advertised.

show run | section eigrp

This will show all commands that are configured under the eigrp processes. Here you can locate the network command you wish to remove and do the following.

enable
conf t
router eigrp X
no network 10.10.10.0 0.0.0.255 (or whatever the network command might be)