[ednog] Using MPLS to replace layer 2 trunking

Vincent Celindro vcelindro at northwestern.edu
Sat Jul 30 00:44:08 EDT 2005

> We've been doing it for about a year, both layer 2 and layer 
> 3 MPLS VPNs.  We prefer to use layer 3 where we can and use 
> layer 2 where we must.  Which right now Layer 2 is used only 
> for two or three legacy VLANs and cross core backhaul for 
> Wireless to authentication boxes in a Data Center.  

We are planning to use this for our quarantine networks.

> The 6500/7600 only supports Port based EoMPLS or 
> Pseudo-Wires, unless you have OSMs.  We are pushing (starting 
> over year ago) for the next-gen PFC to support this, but that 
> is still a little ways off.  There is a way to work around 
> this though, a loop back cable between two GigE ports. one 
> port is configured as a psudo wire Xconnect and the other as 
> a trunk port.  Do this on both the 6509s in your diagram 
> below and you have a virtualised trunk between them. (Yes it 
> is a Hack!!!  But it works!)

I talked to a Cisco Engineer briefly about this awhile ago and I recall him
saying that I would have to use a physical loopback, but didn't catch the
details, since I figured it was well documented somewhere.;) 
I called the tac about this and mentioned the loopback, they of course had
no idea about what I was talking about, go figure. I was hoping someone
would respond with the specifics of the hack, as you said it works.

> The only way to do this is to have a loop-back per VLAN or use OSMs. 

There really aren't any OSMs that appeal to us on a campus environment. I
guess we'll also start pushing cisco for this func. In the next-gen



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