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Isolated Vlan on 6509

We have a campus network of four core 6509 switches in a fully meshed GB configuration. At the access layer we have catalyst 3524 switches in stacks of two. Each stack goes back to two of the core switches (either 6509 switch 1 and 2, or switch 3 and 4). Each 3524 stack has two vlans configured on it so that traffic is load balanced across their two GB uplinks. The campus is configured as one VTP domain, and there are currently 35 vlans. The 6509's route between the vlans using MSFC2's and provide cef switching using PFC2's.

The problem we have is that occasionally, one of the four core switches isolates vlan 1 from all the other core switches. The remaining 34 vlans are still working perfectly ok across all four switches, and only vlan 1 has become disconnected from the rest of the VTP domain.

I noticed that STP information was correctly dispersed for all vlans to all four core switches (including for vlan 1 on the isolated switch). I noticed that CDP information also read correctly on all four core switches. I tried adding new temporary vlans and deleting them, and each time all the vlan information passed correctly between all core switches proving that the 802.1q trunk ports and the VTP propagation worked correctly. It seems layer 2 frames work ok, but layer 3 packets to vlan 1 on the faulty switch do not work.

The version of CATOS on all 6509's is 6.3(3), and the version of IOS on the MSFC2 is 12.1(8a)E5.


Re: Isolated Vlan on 6509


Do you have the dual MSFCs in the core. As I understand you can ping Vlan 1 from the other switches if the device in vlan 1 but you can't ping vlan 1 from the other switches if they are in the different vlan

Can you ping the MSFC interface in the vlan 1 of the isolated switch. Can you ping the switch mgmt interface if it is part of vlan 1 at that time from the other vlan.

Are you running hsrp and if yes, which switch is active for the vlans..



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