Switch MAC address

[bilalccna]

Dear Sir,

In switch ,every ports has different MAC address or one combine MAC address of switch.Is this true?

When we talk about switch'MAC address in STP calculations. Which MAC address STP take either one of the port's MAC address in switch or switch's MAC address (if available).

VTP advertisements are sent over factory default VLAN(VLAN1) using multicast frames. When there is more than one switch, which switches VTP choose to send VTP advertisements?

Please give me details about this. I will be thankful to you.

[kuldeeprawat]

Hi Bilal,

First of all i want to clearify that every Switch port doesn't have it's own mac address it has the memory where it stores the learned mac address on that particular port. You can see more detail by typing show mac address-table in userlevel mode.

The next thing is the address learned by the Gigabit ethernet.

Switch has a single mac address that you can see by typing sh version.

[dave.keith]

Our 2950 switches have a MAC address associated with each port and another for VLAN1. There is no MAC address for Null0. You can verify this by getting the ifPhysAddress values via SNMP. Each switch has a bunch of Cisco MAC addresses, not just one.

On the 2950 I just looked at, the SHO VER command lists a "Base ethernet MAC Address", which it turns out is the VLAN1 MAC address. To satisfy my own interest I captured some BPDUs from the switch I am connected to, and the source MAC on these is the MAC associated with the interface to which I am connected. Then I telneted to the switch, and it used the BASE MAC (VLAN1, where I have the management) for this communications.

The learned MAC addresses used for filtering/forwarding are another thing entirely.

And, it should not matter which address gets used in STP calculations, and they are all contiguous and therefore would be essentially the same value relative to any other devices MAC address. In other words, if the BASE MAC is lower than any other MAC in the network, then _all_ of that switches MAC addresses will be lower than the other devices.

Dave

[pflunkert]

Hi,

the mac-addresses which "owns" the switch depends from the platform. I don't have a really good document, but i know that some switches use the same mac-address a source for all switches. Newer models use for every vlan a unique mac-address. This depends from the switch. On the cat 3750 for example you have a pool of mac-addresses. When you create a vlan, this vlan becomes a unique address from the pool.

I hope this will help you a little.

regards

Peter