[c-nsp] Bridging 802.1q VLANs

[Oliver Boehmer (oboehmer)]

Richard J. Sears <> wrote on Friday, June 30, 2006 4:54 AM:

> I am moving from one office to another and I would like to do it as
> seamlessly as possible.  I'm looking for a way to bridge 802.1q VLAN's
> across a WAN link so that I don't have to move entire VLAN's at once.
> At the current office I've got a NetGear switch (which supports
> 802.1q) as a core switch and at the new office I've got a Cisco 3560
> as a core switch.  The PTP connection between the two offices will be
> 7 T1's terminated at both ends by a single 7204 NPE200 with a
> PA-MC-8T1. We can't afford to put in a GigE connection between the
> two offices or this would be really easy via VTP.  From what I've
> read it looks like there may be a way to do this via VRF or SDE. Has
> anyone else done something similar?

you can use a simple L2VPN config to achieve this. Just plug in the
switches into each 7200 and configure a L2VPN pseudowire between the two
devices. You can run this over IP (using L2TPv3) or over MPLS, I guess
L2TPv3 is what you need. Make sure you increase the MTU on your T1s to
at least 50 byte larger than your Ethernet MTU (for example 1500+50).
The pseudowire configured on the Ethernet port will just take every
ethernet frame (tagged or untagged) and send it to the other end, so the
switches will think it is a direct link between them.
If you want to selectively "bridge" some vlans over the WAN and
terminate others on the 7200 itself, configure the pseudowire on the
vlan sub-interface, and only those frames will be sent.

Take a look at
http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_
chapter09186a00804420e7.html, you basically want to configure something
like this:


ip cef
!
l2tp-class class1
 authentication
 password secret
!
pseudowire-class FOO
 encapsulation l2tpv3
 protocol l2tpv3 class1
 ip local interface Loopback0
!
interface FastEthernet0/0 
 no ip address
 xconnect <remote-ip-address> 123 pw-class FOO

or, if you only want to send certain Vlans over,

interface FastEthernet0/0.10
 encapsulation dot1q 10
 xconnect <remote-ip-address> 456 pw-class FOO

Hope it helps,

	oli