Design tip, redundant gateway!

[runeaagesen]

Dear forum.

I have a layer 3 network, using ospf, no layer 2 between my C3560 devices, please take a look at the attached pdf.

I also have two layer 2 devices, that I would like to connect to this network (these are two Allied Telesyn AT-8024, simple L2 devices).

I also have two available network links frome these L2 devices, but these links are available at site A and D.

What I am trying to do, is:

Host-AA will connect to Host-C (or vise versa), and should be able to do this, even if site A or D is unavailable.

I was thinking of HSRP, but then I have to establish L2 between site A, E and D, something I do not want to do.

I would like to keep a L3/ospf desing in the network.

Do anyone have a sollution/suggestion for desing with these two L2 devices?

Best regards

Rune A

[Dan-Ciprian Cicioiu]

Hello ,

I would try using HSRP between A and D L3 switches , and the host A vlan  transported between A and D location on layer 2 link.

The only problem is that you will have the layer 2 link ,a critical one => if the link goes down , there will be some issues between host A and C (for example).

Then the best way , using this setup , will be to advertise the Host A prefix with a cost better from A router,then from the router D, and also the A router being the HSRP active. This way the D router will be used only if A fails.Also to cover all uplink loss of the router A you will have to do some HSRP tracking , based on some interface status , or routes in the routing table , this way if A router will have both uplinks down/ospf adj , it will not be the HSRP active.

Dan

[runeaagesen]

Hi, thanks a lot for your answer.

Yes. was afraid that HSRP was the sollution, because we've been reconfigured our network from a L2 to a L3 network, except from a few L2 devices.

I've been struggling with stp/rstp/mst for years, and was hopeing to drop L2 and use ospf for redundancy in our network.

I'll give it a try.

Rune