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New Member

Stacked VLAN Bridging + PPPoE

I have a connection to a BRAS setup that needs stacked VLANs, 660.1 to 660.10

I'm not connecting to the BRAS yet, as I'm first trying to sort out the appropriate config.

So what I'm doing is I have 2 PCs one running wireshark and another one starting the PPP session. These PCs then connect into a 7204VXR

My the port config is:

interface FastEthernet1/0

no ip address

duplex full

!

interface FastEthernet1/0.660

encapsulation dot1Q 660 second-dot1q 1

bridge-group 60

!

interface FastEthernet2/0

no ip address

duplex full

bridge-group 60

!

My assumption was that the PPPoE discovery frames would come into Fa2/0, bridged across to Fa1/0.660 and get sent out with the both vlan tags set.

The wireshark pc is reporting seeing PPPoE discovery packets, but only with the first vlan tag, not the second.

Any idea why the second vlan tags aren't being applied?

2 REPLIES
Hall of Fame Super Silver

Re: Stacked VLAN Bridging + PPPoE

Hello Matthew,

the usual scenario for stacked Vlans involves the use of a LAN switch with a dot1q tunnel that adds the external vlan tag to an already tagged frame.

So I think it's difficult to get a double stack at once.

What is the outgoing interface ?

I've found a reference to the command

http://www.cisco.com/en/US/docs/ios/lanswitch/command/reference/lsw_b1.html#wp1018095

The following example shows how to terminate a Q-in-Q frame on an unambiguous subinterface with an outer VLAN ID of 100 and an inner VLAN ID of 200:

Router(config)# interface gigabitethernet1/0/0.1

Router(config-subif)# encapsulation dot1q 100 second-dot1q 200

The following example shows how to terminate a Q-in-Q frame on an ambiguous subinterface with an outer VLAN ID of 100 and an inner VLAN ID in the range from 100 to 199 or from 201 to 600:

Router(config)# interface gigabitethernet1/0/0.1

Router(config-subif)# encapsulation dot1q 100 second-dot1q 100-199,201-600

It looks like that this command expects the frame to be already double tagged and to extract it for further processing and not to set the tagging.

In other words this could be the config on the BRAS side.

Hope to help

Giuseppe

New Member

Re: Stacked VLAN Bridging + PPPoE

The outgoing interface is FastEthernet1/0.660.

I'm using an unambiguous sub-interface, as I'd declared "second-dot1q 1", but this is obviously not working.

I'll grab a spare switch and see if I can get the switch to add the first tag and the 7204 to add the second.

Cheers,

Matt

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