Switch mac address learning

[max.logon]

I was curious, we have two switches connected to eachother through an access port and on one of the switches there is an AP.  Now the switch that is connected directly to the AP should learn mac addresses of the wireless clients, but will the second switch learn those addresses?  This is assuming that the same VLAN is being used on both switches.

Also, if that port was a trunk instead would the second switch learn of the mac addresses of the wireless clients?

In both cases I would think not, but would like to get this confirmed either way.

thanks

[Giuseppe Larosa · Accepted solution]

Hello Max,

as soon as the wireless clients send out a broadcast frame the second switch will learn of them regardless of the type of link between the switches (access port or trunk it is not important). This is because broadcast traffic is propagated everywhere in a broadcast domain.

The key point is that the same broadcast domain spans on both switches.

Hope to help

Giuseppe

[Jon Marshall · Accepted solution]

switch A connected to switch B on int gi0/1

switch B connected to AP on int gi0/2

switch B will learn the mac-addresses of the clients from the AP and record then against gi0/2

switch A will learn the mac-addresses of the clients from switch B and record them against gi0/1

this is assuming as you say that it is all one vlan. It has to work like this ie. both switches need to record the mac-addresses to interface/port in the mac-address tables otherwise they would have to broadcast all traffic for the AP clients.

Jon

[max.logon]

thanks for the quick response!

[iptrix]

I'm having a case now where switches don't learn mac addresses, specifically from DHCP Discover messages that are broadcasted. That means that the unicast reply asked for has no path!

And it's not just on the distribution switches, or the core DHCP server (a 3750), but even one more client switch that the message has to pass. They aren't learning mac address from DHCP packets -- why?

/Micke