On one of our sites, we have two 6509 with MSFC1/SUP1. We have 32 VLAN configured on the routers and switches, we also have HSRP configured, one group for each VLAN. Router 1 (R1) is the active router for all odd VLANs, R2 is the active router for all even VLAN, and today we lost access to the site for about 15 minutes, when we checked the router log we saw these messages
Dec 11 11:23:57 R1 139: Dec 11 11:23:56.654 est: %STANDBY-3-DUPADDR: Duplicate address 10.1.15.3 on Vlan17, sourced by 0000.9999.0017
Dec 11 11:23:59 R2 895: Dec 11 11:23:58.232 est: %STANDBY-3-DUPADDR: Duplicate address 10.1.15.4 on Vlan17, sourced by 0000.0002.0017
The first message from R1, the IP address from the message is the VLAN IP address and the MAC address is the standby MAC address. The second message from R2, the IP address is the VLAN IP address and the MAC address is the configured MAC address on the interface.
Then all the VLANs changed state from (standby to active) except VLAN17, sh standby shows it didnt change state on any of the 2 routers.
Interesting problem. Here is a probable cause, altough one needs to know more about the topology of the network to exactly pinpoint the cause. It looks like you have had some kind of loop in the network. This loop can have caused duplicate packets on vlan 17. As a result of this loop, the network has split due to spanning tree.
The latter, in turn, has caused all other HSRP-pairs to switch to active state on both core-switches. vlan 17 remained operational because it was looped.
I suspect that someone has misconfigured something, or connect a device to the wrong ports. Then after 15 mins he noticed that the network was down and removed the device, appearently without giving notice.
Let me know what it was when you have solved this one!
I agree it looks like a spanning tree loop, however as I mentioned in my orginal message we have BPDU guard enabled, so if one if the user connected a hub or anything that will disable the port immediately..
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