Mac address-table command

[PietroPoliseno27977]

Hi everyone I have two switches connected with a gigabit link. When I clean the mac addrress table on switch "A", and run the command "show mac address-table dynamic", I notice that the clear command has deleted all the other entries of the connected devices, but not that of the direct connection with switch "B" and then it appears: "" "Vlan Mac Address Type Ports
---- ----------- -------- -----

1 0001.9654.151a DYNAMIC Gig0 / 1 "" "" "" "

1) Why?
2) Is the mac address the mac address of switch "B"? That is, to reach the mac 0001.9654.151a I have to go through the Gig0 / 1 port of switch "A"?

[balaji.bandi]

check the MAC Address belong to  ?

[Martin L · Accepted solution]

well, basic control traffic flows between those 2 switches; at least CDP and STP.  Frames must have source (interface) and destination addresses (specific M-cast).  you have trunk between them and at least 1 vlan on (probably default vlan 1).  In this case, MAC is of interface of opposite switch that is a trunk (used to trunk , aka connects 2 switches).  Switch must use some sort of ID for control traffic like CDP, STP, etc.

if you add more vlans, same MAC is used for different vlan IDs because of per-vlan STP.  If you capture traffic, you can see multiple frames with your switch source MAC and interface Id while destination is M-cast address.

Regards, ML
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[PietroPoliseno27977]

I checked it is the other switch's gigabit interface mac which is enabled as a trunk port thanks