Mac address dynamic and static

[N W]

Hi Guys

Have a question.

sh mac address-table address

When it comes up with with static and dymanic

Can someone explain the difference?

I say one way and my collegue says another thing.

Not going to say anything...

Please help settle a bet....

Noel

[cadet alain]

Hi,

static mac is a mac you configured on the switch vs dynamic which is one learnt from the src mac add field in the ethernet frame traversing the switch.

But there are also special mac addresses used by the switch for internal purposes which are also static like the one used for making up bridge id used in STP( when doing a show mac they appear with a CPU next to them).

Regards.

Alain.

[N W]

like port security???

Not like the one thats in the switches CAM table......

[Latchum Naidu]

Hi Noel,

A Static MAC address is one that has been manualy input (typed via a command) into the CAM or MAC address table.

A dynamic MAC address is one that has been learned via an arp request.
For example if a switch learns the MAC address from another device then it has dynamically sourced the MAC address.

Say Computer A is connected to Switch-1, Switch-1 is connected to Switch-2
Now you issued command "#sh mac-address-table" in Switch-2 it will learn the Computer A mac address dynamically from Switch-1

#sh mac-address-table
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
All    0180.c200.000e    STATIC      CPU
All    0180.c200.000f    STATIC      CPU
All    0180.c200.0010    STATIC      CPU
All    ffff.ffff.ffff    STATIC      CPU
594    0001.6c58.486e    DYNAMIC     Gi1/0/3
594    0001.6c58.5606    DYNAMIC     Po6

Please rate the helpfull posts.
Regards,
Naidu.

[N W]

If you plug a PC into switch one and issue sh mac address table.

Should it read static or dymanic considering its not being learnt from a different switch but it known because it is directly connected

[cadet alain]

Hi Naidu,

A dynamic MAC address is one that has been learned via an arp request.

They could also be learned via arp replies and also by other type of traffic

Regards.

Alain.

[cadet alain · Accepted solution]

these  could be static ones indeed if you manually entered them into port-security config but they can also be configured directly in the CAM table  this way:

mac address-table static mac-address interface vlan vlan-id [drop]

Regards.

Alain.

[tech_gubby]

Can you please tell me why/when static mac address entry is required in switches?

[Andy K]

I can answer this one,  up to now in our network, the only time I had to put static MAC in the switches was for devices that talk very rarely or have no keep-alives, like TOA wallphone devices, when you press the button to call another station, the first call never made it, but once you press the button twice then it worked. Sort of like the first ping often doesnt reach destination because the MAC dissaperead along the line.  And also some Ingenico payment machines, the first transaction didnt always pass so by forcing those MAC to their vlan it solved everything.