Imagine a topology with Switch A and Switch B trunked together. Also imagine a router on a stick attached to Switch A that routes for these VLANs. The VLANs are as follows:

 VLAN 1 =
 VLAN 2 =
 VLAN 3 =
 (private-vlan primary
  private-vlan association 4)

 VLAN 4 = isolated private vlan, same subnet as VLAN 3
 (private-vlan isolated)

The router on a stick contains the following interfaces:

 G0/0 = trunk
 G0/0.1 = (vlan 1)
 G0/0.2 = (vlan 2)
 G0/0.3 = (vlan 3)

How would I configure the trunks to pass both normal and VLAN traffic?

Will putting the trunk port between Switch A and B and Switch A and the router as:

 switchport mode private-vlan trunk promiscuous

stop the trunk from passing traffic for Vlans 1 and 2? How can I configure the trunks to do these things. I would like to specify the trunk allowed vlans if possible.

  • Were you able to make it work? I have similar requirements and it seems to be not working or not supported on 3560x atleast. – user319118 Oct 28 '15 at 8:28

Interesting question, but it seems possible. Might not be a bad idea to lab it first, but you could probably test it quickly (and if it messes anything up, you can fix it quickly).

You can extend PVLANs across switches with the use of trunks. Trunk ports carry traffic from regular VLANs and also from primary, isolated, and community VLANs. Cisco recommends the use of standard trunk ports if both switches that undergo trunking support PVLANs.

I don't think you need to do anything special on the trunk ports, aside from adding it as an allowed VLAN and then configuring the private vlan on the other switch. You would also trunk it into the router like you would a normal VLAN.


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