Duplicate IP Address on Cat6509 MSFC

Unanswered Question
Feb 11th, 2007

Anyone have faced this log message of duplicate IP address before?

Here is the network topology

C6509CS01 --------------- C6509CS02


This problem occured for 5 min and brought the customer vlan 1 network. Note that the


Feb 8 08:08:32: %STANDBY-3-DUPADDR: Duplicate address on Vlan1, sourced by 0000.0c07.ac09

VLAN 1 MAC address on C6509CS01

Vlan1 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 0009.b63e.cffc (bia 0009.b63


*Feb 9 01:29:49: %STANDBY-3-DUPADDR: Duplicate address on Vlan1, sourced by 0009.b63e.bffc

VLAN 1 MAC address on C6509CS02

Vlan1 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 0009.b63e.bffc (bia 0009.b63e.bffc)

Internet address is

I am suspecting this is a spanning tree loop and causes the switch to see a duplicate IP address. But logically, there is no loop between the 2 6509 unless the port-channel connecting the 2 switches fail and in turns there is a loop. But in this cases, STP should kick in.

Anyone have any solution?

I have this problem too.
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bhedlund Sun, 02/11/2007 - 19:00

What version of IOS? There are some nasty Etherchannel bugs in 12.2(17)SX and earlier code where the switch reflects packets back to itself.


DaturaX88 Sun, 02/11/2007 - 19:19

The switches are running in hybrid mode.

Here are the IOS versions

CatOS: 7.1(2)

MSFC: 12.1(11b)E

scottmac Sun, 02/11/2007 - 20:00

I've heard of this happening when multiple non-Cisco Wireless Access Points (Symbol specifically) were connected to 6500s and they didnt hand off a roaming client fast enough / properly ... so the switch would see the same MAC on two diffeent ports at the same time.

I think it also may show up as port flapping.

Other than that, I haven't seen / heard of it.

Good Luck


owaisberg Thu, 02/15/2007 - 10:58

That is HSRP configuration issue. Make sure

your HSRP group numbers on both routers match.



d_monaghan Sun, 02/18/2007 - 16:08

As said above check your etherchannel configurations. I had a similar problem when upgrading from hybrid to Native on two 6509s.

I had set one side to 'on' and the other to 'desirable' and I got the same error messages, and it brought everything down. Once we changed both sides to 'on' everything was fine. I don't think it is an HSRP problem, it is an STP problem as you say, it is seeing its own hsrp multicasts many times over.


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