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7600/6500 -L3 MAc-address

Hi Guys,

7600/6500 with SUP720 use same MAC-address for all layer 3 Port which is not from the pool of mac-address allocated to line card rather it use SUP mac-address...

This was a not a case for sup1/Sup2 , Does Any know the reason of this feature of having same-mac address on all layer 3 physcial interface ? what is an advantage of this ?



Hall of Fame Super Silver

Re: 7600/6500 -L3 MAc-address

Hello Chintan,

possible advantages:

less MAC addresses are used to carry L3 switch originated traffic.

if you connect two different interfaces of the same device they shouldn't exchange packets and shouldn't build adjacencies even if they are in different VRFs (you need to change the mac address on one with an explicit command)

It goes on the direction to be "SVI oriented" where it makes sense to refers to Supervisor.

Hope to help


New Member

Re: 7600/6500 -L3 MAc-address

Hi Giuseppe,

Thanks for all time help. I also had same thought but not sure if there is any other reason.

By the way, I have small doubt on VTP :


I have some switches running server/client mode. In case I want to chagne VTP mode to transparent, Can i straight away go ahead in production netowrk ? Will that impact any way on existing VLAN database of client/server switch ?

Hall of Fame Super Silver

Re: 7600/6500 -L3 MAc-address

Hello Chintan,

about moving switches to transparent mode the important advice is:

check that all devices are configured and running VTP version 2:

the reason is that VTPv1 transparent switches don't allow VTP frames if they contain a VTP domain different from their own.

With VTPv2 this limitation has been removed.

I see that you want to move all switches to transparent mode.

I'm not sure about the clients, the servers should keep their Vlan database.

I've seen some small switch like C2950 moving itself to VTP transparent because the max number of vlans (128) has been exceeded on the VTP server, it had some vlans up to 128 on it also after.(I should check it was some years ago )

Hope to help


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