Issues with routing and spanning tree in 6500 with MSFC network

Unanswered Question
May 15th, 2008

Hello all

I got a complex issue with link redundancy in my core network. As shown in diagram, I have four 6513 (A,B,C,D) switch with CatOs and MSFC IOS in hybrid mode and two 6509 switch. Switch E has MSFC but Switch F doesn't have it. There are more than two hundred vlans and each 6500 switch are working as VTP servers with more than 70 4000 and 4500 series switch.

Switch A,B,C,D, E are configured to intervlan routing with EIGRP routing protocols. Switch A and B are HSRP pair for 30 vlan and switch C and D are working as HSRP pair for rest of 100 vlans, and switch E have inter-vlan routing for 50 and more vlans with out hsrp configuration.

Switch A, B, c, D, E are in RAPID PVST + mode and switch F and rest of the access layer switch are in PVST + mode of Spanning Tree.

My concern is the effect of connecting all the redundant link as shown in proposed diagram.

Does STP will come on the way of EIGRP shortest path possibly blocking a port on the way ?

I just wanted to know issues that come along with my proposed connectionbefore going live.



I have this problem too.
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subharojdahal Thu, 05/15/2008 - 06:48

I would really appreciate any PRO will have to say somethings on my scnario.

That's a big project you have there. My advice is to find a way to lab it up. Your local Cisco SE might be able to hook you up with a Cisco lab. I'd say book some time with a CCIE rack rental company but your deployment is bigger than most CCIE lab racks. Honestly, for a network of your size you should have some lab of your own to model at least a subset of your environment. 8 or so used 3650s is a drop in the bucket compared to the value of what you have deployed and a small price to pay for piece of mind when you make changes that could bring your entire enterprise down. That said, if you can't find a lab or build one yourself it's time to call in help (see below)

I know that's not the technical answer you're looking for but this project looks to be bigger than something that can be handled in a forum setting. Quite frankly, this is something that many people on this forum make a very good living doing and giving away a solution/design would be taking food out of their mouths. Answering a question about VTP pruning is one thing, this is something else.

Best of luck to you.

subharojdahal Thu, 05/15/2008 - 09:56

Thanks lot for suggestion. I understand your concern and complexity of solving the problem at this forum. I just wanted to know how how packet is forwarded from one switch to other as there are both trunk link and routing protocols.

Let say N1 node in vlan 5 is connected to switch A and other node N2 on same VLAN is conneted in switch B. So, how packet forwarded from N1 to N2 if both trunk link as well as EIGRP route is there.

subharojdahal Thu, 05/15/2008 - 10:56

thats right. Let me twist the my issues. I have server farm on vlan 25 and conected with switch C. I have a node N1 on vlan 10 on switch A wants to access server S1 in vlan 25. The switch A has two trunk link to switch C, one is directly connected to C and other is connected via D. Each trunk link allows vlan 25.

If node N1 want to access S1, Switch A sends the traffic to both trunk links, only one link ( possibly due to stp ??) or let the EIGRP to decide ??

If it sends both the trunk links, then swich C will send same frame towards D, or D will send same frame towards C, eventually creating layer two loop.

Please help me to clear from the concepts

t814687 Thu, 05/15/2008 - 12:12

Hi Subharoj , My advice will be to do an analysis and separate L2 and L3 so you can draw a L3 diagram of your network keeping into account the STP blocked ports for each VLAN. You should clearly know what switch is a STP root on your network and this has to be documented.

This way you will be able to see how the traffic will be flowing. When your L2 topology changes L3 will re-converge accordingly. But again without clear L3 view it's hard to make any advices here.


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