EIGRP using SVI and metric manipulation

[Glenn R]

Hi,

I have a question around EIGRP path manipulation for WAN links to prefer the best path for the better link and then have the secondary link configured so that it is a feasible successor.

The issue I am facing is how to manipulate the path costs for one of the links. The configuration is as such that the switch I am using has SVI's configured and added to the EIGRP AS for advertising. There are two different supplier routers which participate in EIGRP which are also in that same VLAN as the primary SVI. My issue is that EIGRP routes for both ISP devices ad been advertised in via the VLAN and there is no distinction. 

How would I go about manipulating this ???

Some config output below:

      172.25.0.0/16 is variably subnetted, 41 subnets, 4 masks
D EX     172.25.0.0/16 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.0/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.4/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.8/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.12/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.16/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.20/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.24/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.28/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.32/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.36/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.40/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.44/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.48/29 [170/3072] via 172.31.240.1, 01:38:49, Vlan245
D EX     172.25.0.56/30 [170/3072] via 172.31.240.1, 01:38:49, Vlan245

DIDS-6880#sh ip eigrp topology all-links 
EIGRP-IPv4 Topology Table for AS(100)/ID(172.31.240.3)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status 

P 172.29.151.0/24, 1 successors, FD is 3072, tag is 14, serno 2006
        via 172.31.240.1 (3072/2816), Vlan245
        via 172.31.240.2 (269056/268800), Vlan245
P 172.19.56.0/24, 1 successors, FD is 3072, tag is 14, serno 1793
        via 172.31.240.1 (3072/2816), Vlan245
        via 172.31.240.2 (269056/268800), Vlan245
P 172.25.51.16/30, 1 successors, FD is 3072, tag is 14, serno 1986
        via 172.31.240.1 (3072/2816), Vlan245
        via 172.31.240.2 (269056/268800), Vlan245
P 172.25.192.100/30, 1 successors, FD is 3072, tag is 14, serno 1992
        via 172.31.240.1 (3072/2816), Vlan245
        via 172.31.240.2 (269056/268800), Vlan245

[jj27]

I've had good luck implementing delay on my SVIs in previous occasions. Not sure if it is the best method, but it works.  Add a significant amount of delay to the SVI at the lesser preferred path. That should manipulate the routes enough.

interface vlan xxx

delay 50000

[Glenn R]

Hi,

I don't think i have quite explained myself correctly as what you have suggested will not work. Let me try again.

We have a 6880 switch that has SVI 100 configured with ip address 172.16.0.3.

Then there is ISP-1-2900 router that is connected to Gi1/0/1.

The port configuration for gi1/0/1 is :

interface Gi 1/0/1

switchport mode access

switchport access vlan 100

ISP-2-2900 is then connected to Gi 5/0/1 and the port configuration is:

interface Gi 1/0/1

switchport mode access 

switchport access vlan 100

EIGRP has the 172.16.0.0 0.0.255.255 network included as well as redistribute connected option.

What I need to do is change the metric that ISP-2 comes in on so that it is more inline with ISP-2 so that teh route has a feasible successor.

Hope this explains it better 

Glenn

[Richard Burts]

Glenn

I think that some of your decisions about how to configure your network are preventing you from accomplishing what you say that you want, which is to differentiate EIGRP routes over the two WAN links. What you have created is a single layer 3 connection between sites. As far as EIGRP is concerned there is a single connection between the sites.

Remember that EIGRP is looking at things from the perspective of layer 3 and can only process on layer 3 interfaces. You have a single SVI for EIGRP and one logical path between sites. The 2 links are configured as layer 2 links and so EIGRP can not be aware of them or differentiate how traffic is forwarded over them.

I am a bit curious how the 2 2900 routers are configured to make this work. And I am a bit concerned that information given in your second post is inconsistent with the information given in the ouputs contained in your first post.

HTH

Rick

[Glenn R]

Hi Rick,

Thanks for the response. 

Just ready through the second post and the information I missed typed was the second ISP connection which is on interface 5/0/1 rather than 1/0/1. 

Regards

Glenn

[Richard Burts]

Glenn

The difference between interface 5/0/1 and 1/0/1 is insignificant and not at all what I was talking about. In your original post you show routes learned via vlan 245 but your second post shows vlan 100. And your first post shows a neighbor at 172.31.240.1 but your second post show subnet 172.16.0.3. Those are the inconsistencies that concern me.

HTH

Rick