Turning ON EIGRP on layer3 distribution switch

[Ricky Sandhu]

Hello everyone, I have an EIGRP related question that I am a bit stomped on. Just to give you a brief overview of my network setup: I am running a Hub and Spoke network with 1 hub and approx. 40 spoke routers. The hub router (HUB1) is located at our data center and connects to the internal data center network via a layer 3 stack switch. For redundancy I have added another Hub router (HUB2) at the data center connecting to the same layer 3 switch. My network is running EIGRP. On the layer 3 switch I have static routes pointing to the HUB1 router for all spoke networks. Obviously this is not scalable incase of a hardware failure on HUB1 and beats the purpose of having HUB2. Therefore I have decided to remove all static routes from the layer 3 switch and turn on EIGRP on the switch itself. I tested this configuration in my lab. I discovered when I turn on EIGRP on the layer 3 switch, I get two routes with same metric to a given spoke router (SPOKE1). SPOKE1 connects to both HUB1 and HUB2 over a DMVPN network via Tunnel0 and Tunnel1 interfaces over the Internet utilizing a single high speed internet connection. Now with EIGRP turned ON, my layer 3 switch knows about SPOKE1 via both HUB1 and HUB2 with the same metric (see below). I dont' want to turn this ON in my production network due to the fear of out of sequence packets to and from my layer 3 switch. I am still learning about EIGRP as I go along.

What can I do so that my switch can rate one router different over another and utilize one route for all traffic until a failure occurs?

sw-q9-1#sh ip route

Gateway of last resort is not set

D    192.168.1.0/24 [90/156416] via 172.18.123.3, 00:20:13, Vlan123

                    [90/156416] via 172.18.123.2, 00:20:13, Vlan123

ALSO

sw-q9-1#sh ip eigrp top

EIGRP-IPv4 Topology Table for AS(1)/ID(172.18.123.250)

P 192.168.1.0/24, 2 successors, FD is 156416

        via 172.18.123.2 (156416/156160), Vlan123

        via 172.18.123.3 (156416/156160), Vlan123

[John Blakley]

Ricky,

You can change the delay on the router that you want as a secondary. If you're wanting all routes from HUB2 to be the secondary routes and not in the routing table, you can change the delay higher than what it is now. You'll want to change it just enough to where the routes aren't showing up in the routing table, but they're still listed in the topology table as a feasible successor.

HTH,

John

Please rate all useful posts...

[Ricky Sandhu]

Hi John, thanks. I will try that out and report back.

[Ricky Sandhu]

Also is it useful to make this switch an eigrp stub? Will it still advertise the local VLANs (since they are connected)?

[John Blakley · Accepted solution]

Ricky,

Yes. By default, it will advertise connected and summary routes to the neighbors as long as you have network statements that match those vlans.

HTH,

John

[kunalgandhi · Accepted solution]

Dear Ricky,

As per my understanding, you want to utilize only one route at a time and keeping another path (even of same metric) available as backup all the time immediately after the primary path fails.

In your current scenario, receiving the route for destination 192.168.1.0/24

from two path with the same metric.

Use command ' maximum-path 1 ' on your sw-q9. This configuration put only one path per destination in routing table even if same metic paths available in eigrp topology table( caution: applied on entire routing table ) .

When one path fails, immediately put another path in to routing table.

I have tried EIGRP load balancing with this command in GNS3 & achived the desired result.

Hope that clarifies things.

Waiting for ur responce...

[Ricky Sandhu]

Hello Kunal, thank you for your post. Can you advise which option is more beneficial over the other? I.e. using higher delay or maximum-path command.

[John Blakley]

Ricky,

Delay will affect all routes coming from HUB2 and change metrics. Maximum-paths, admittedly I didn't think about changing this one, will allow your metrics to stay the same but only put 1 route in the routing table. Overall, I think maximum-paths may be the better of the two options. If you ever need more routes in the routing table though, you'd have to change max-paths to something that would be greater than 1.

HTH,

John

[Ricky Sandhu]

Thanks gents. That worked.