Layer2 over Layer3

Philip Lavine source_route at
Fri Sep 14 22:05:53 UTC 2012

If the psuedowire is setup to allow a vlan to be exteneded, but the vlan is already extended over a dedicated link, how will spanning tree behave? Right now I have it setup and I dont see the psuedowire trunk in a blocking state. Will the switch that has both the pseudowire trunk on it and the dedicated link know how to forward the frames if either goes away?

 From: David Swafford <david at>
To: Paul Vinciguerra <pvinci at> 
Cc: Philip Lavine <source_route at>; NANOG list <nanog at> 
Sent: Wednesday, September 12, 2012 7:46 PM
Subject: Re: Layer2 over Layer3
Hey Philip,

Any Transport over MPLS will do this too.  Here's a link to an example
setup of two sites where just L3 connectivity exists between them:  In that setup, I have just
IPSEC VPN connecting the two locations, but have an 802.1q trunk
extended between both.  In the example configs, Fa0/1 on both ends is
a transparent L2 connection.  The boxes used here were 3725s on 12.4T.


On Wed, Sep 12, 2012 at 3:37 PM, Paul Vinciguerra
<pvinci at> wrote:
> ASR supports OTV if you can do multicast over L3.  Although, you may not need L2 extensions in the end.
> -----Original Message-----
> From: Philip Lavine [mailto:source_route at]
> Sent: Wednesday, September 12, 2012 6:23 PM
> To: NANOG list
> Subject: Layer2 over Layer3
> To all,
> I am trying to extend a layer2 connection over Layer 3 so I can have redundant Layer connectivity between my HQ and colo site. The reason I need this is so I can give the "appeareance" that there is one gateway and that both data centers can share the same Layer3 subnet (which I am announcing via BGP to 2 different vendors).
> I have 2 ASR's. Will EoMPLS work or is there another option?
> Philip

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