2960 to 3850 MAC Address for interface and vlan appearing in connected switch

[Billm]

Is it normal for a switch to have both the interface bia MAC address and the VLAN MAC address of the connected switch in its table?

I have a 2960 connected to a 3850 in a trunk. The 2960 has a layer 3 vlan(20) configured with an IP Address. I connect this switch to the 3850.

2960 interface config:

interface GigabitEthernet1/0/47
switchport trunk native vlan 20
switchport trunk allowed vlan 5,20
switchport mode trunk
end

3850 interface config:

interface GigabitEthernet1/0/1
switchport trunk native vlan 20
switchport trunk allowed vlan 5,20
switchport mode trunk
end

The mac table on the 3850 shows:

C-M-3850-CoreStack#sh mac add int g1/0/1
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
20 bcc4.93ae.c32f DYNAMIC Gi1/0/1
20 bcc4.93ae.c354 DYNAMIC Gi1/0/1

the .c32f is the bia on g1/0/47 of the 2960

the .c3534 is the VLAN 20 mac of the 2960.

I am having connection issues beyond my switch infrastructure. I can connect from the switch but can't ping or ssh from a workstation.

Is this normal for the switch to have both MACs in the table?

[Richard Burts · Accepted solution]

Yes that would be normal behavior. Remember that the switch builds and maintains its mac address table (layer 2 forwarding table) by examining each Ethernet frame that it receives and checking the source mac address. So if your switch receives a frame generated by the other switch (perhaps a CDP frame or spanning tree or something like that) the source mac address would be the interface mac and your switch puts that entry into its mac address table. Then your switch receives a frame that is an IP packet forwarded by the SVI or the other switch. The source mac for this frame would be the mac of the SVI and your switch puts that mac into its table also. Since both frames were received on the same interface then that interface is associated with both mac addresses in the table.

HTH

Rick