Different default routes on 3750 VLANS

[Phil Bradley]

Hello All. I have a scenario where I have two 3750 stacks tied together at different locations. I have different ISP's at each location and would like to route traffic based on vlan. For example, at location 1 I want only vlan10, 20, and 30 to go out location 1's ISP. Vlan 50 should go out locations 2 ISP. I currently have an ip route 0.0.0.0.0 0.0.0.0.0 10.x.x.x at location 1, which is ISP 1's  gateway. I have tried to use the ip route 0.0.0.0 0.0.0.0 vlan 50 10.x.x.location2 router address, but vlan 50 still will use the global static route. Is this possible with per vlan default gateways or do I need to use policy based routing to accomplish this?

[John Blakley]

You would probably need to configure pbr for this to work. The global default route is used by the system to route traffic from all vlans out to a next hop. To override that behavior, you'd need to configure pbr and match on the subnets that you want and apply them to their respective vlan svi.

To support pbr if you don't already have it enabled, you would need to change your sdm to routing. To see your current one, you would type: "show sdm prefer". If you have 0 by policy based routing aces, you'll need to change your method. To change to support pbr: "sdm prefer routing". You'll need to reload the switch for the change to take effect though.

HTH,
John

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[Phil Bradley]

Thanks John. This will get me started in the right direction. What does the command IP route 0.0.0.0 0.0.0.0 vlan x x.x.x.x actually do?

Also, do you need a certain image to be able to do pbr on the 3750?


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[John Blakley]

It's a failover type route. The trick is that the address that you point to will be used, but if it goes away it will arp for a next hop via the vlan interface so you wouldn't lose connection should your next hop be on that vlan. So, you could have two default routers on the vlan and statically pointing to one of them. If that one dies, the next one could be used as long as it knows how to route your traffic out of the network.

Here's a good document explaining it:

http://cisconinja.wordpress.com/2009/04/05/static-routing-differences-between-specifying-an-exit-interface-an-ip-address-and-both/

I'd have to look around to see if I can find any documentation on the minimum requirements. I would suggest trying to change your sdm template. If you can, I would think it would be supported.

This post seems to indicate that you need a minimum IP Services image:

https://supportforums.cisco.com/thread/2180326

HTH,
John

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[Phil Bradley]

Thanks. I verified I have the default PBR and I also have the IP base image. I will need to update to the IP services to accomplish this. I will go ahead and mark your answer correct since I will not be able to test this without an upgrade. I am certain that PBR will do what I need though. Thanks.

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[devils_advocate]

Hi Phil

I would look at Route Maps for this purpose.

Off the top of my head, I would think an ACL for each LAN subnet and a Route Map which changes the next hop IP address depending on the source IP address of the packet.

Thanks

[Phil Bradley]

Thanks for the info. Unfortunately I do not have the proper IP services image to do this. I only have the IP base which does not allow policy based routing.



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