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Problems routing between 2 6509's (redundant MSFC's in each)


I'm trying to route between 2 6509's using Gige, fiber. Trunking is turned off, a traffic Vlan is configured on each side with associated routed interfaces on each swtich with same IP subnet. Everything looks great from a routing perpsective except that the interfaces are flooding the switch with ARP requests causing all the switches to come to a crawl (CPU utilization 90%). When I investigated a little it seems when I do a sho arp for the VLAN interfaces it is showing not only their own IP and MAC info but the other side as well. I'm running in hybrid mode. Do I need to run native OS to get this to work? What I'm hoping is to have two routed paths (1 Gig) each between the two switches for an on campus fiber network. I thought this would be easy but strange things are happening and I can't get it to work right. Please help. I need it up and running in 2 weeks. I do not want to bridge.

Thanks for your help.



Re: Problems routing between 2 6509's (redundant MSFC's in each)


You do not need to run Native to get this to work. What you should have, for your point to point links between the Catalysts, is a VLAN configured on the sup which these links are in. For two point to point links you'd have two VLANS on each sup with one link in each. On your MSFC you configure a VLAN corresponding to your SUP Vlan (where your point to point links are members only). Your symptoms sound like you've got a bridging loop of some kind but this is just a guess with the information you've provided.

Hope this helps you,


New Member

Re: Problems routing between 2 6509's (redundant MSFC's in each)

HI there,

I did as you said and I can get one point to point link to work. For the second, I get that to work however the 1st MSFC doesn't see the 2nd MSFC's connection (within the chassis) as a route. What I'm trying to do is load balance between two point to point connections using the two MSFC's within each chassis. So for example, I would like to have this:

1st switch 2nd switch

1/1 VLAN 8---------------------------------1/1 VLAN25 MSFC1

2/1 VLAN 9 -------------------------------- 2/1 VLAN26 MSFC2

On the first MSFC, you see VLAN 8 and 25 as valid routes but not VLAN 9 or 26. I want EIGRP to recognize these as two valid paths for use.

Right now I've resorted to using Spanning Tree with 1 port blocked like this:

1/1 VLAN 8 1/1 VLAN25

2/1 VLAN 8 (standby) 2/1 VLAN25 (standby)

It seems most stable. Everything else I've tried has caused me terrible loops.

Thanks for your help!


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