Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

mac address table on C3750

I have problem with mac address learning on C3750. I need to connect two vlans on the same C3750 by external L2 box (IPS device). This box provides mapping between vlans on trunk ports. Connection is depicted below:

int vlan 370 (L3 svi interface)


g1/0/20 (trunk with vlan 370)


external box, maps vlan 370 to vlan 361


g1/0/19 (trunk with vlan 361)


another switch


PC (in vlan 361)

But this does not work. C3750 refuses to learn mac address from L3 interface vlan 370 on interface g1/0/19 in vlan 361. When I use command 'mac-address-table static xxxx.xxxx.xxxx vl 361 int g1/0/19' all is working correctly. But I can not use this, because mac address of SVI interface changes after each C3750 reload.

Any suggestions are greatly appreciated.

New Member

Re: mac address table on C3750

I'm not sure how the external L2 box works, but maybe you have to use the 'native vlan' command on Gi1/0/19 and -20 with 370 and 361 as native vlans?

(The native vlan is transmited untagged in a trunk)

I'm not really confident about this but maybe you want to give it a try...

New Member

Re: mac address table on C3750

That box supports 802.1Q and provides mapping from tag 370 to tag 361.

In fact I need to connect more than one vlan thru, so native vlan is not usable.

I guess that C3750 refuses to learn mac address pertaining to int vlan 370 from external wire.