[j-nsp] l2circuit or l2vpn

[sthaug at nethelp.no]

> The main differences are related to the Martini and Kompella method of 
> implementing the technology. For example l2vpn is based on MBGP with RSVP 
> doing the LSP signaling and advertising the labels.  This means that the 
> path of the circuit is handled as if it were a virtual circuit because 
> RSVP signals and reserves the bandwidth before traffic is passed. 
> l2circuit is based on LDP which sends hellos end to end but depends on the 
> IGP for resource reservations.  The data forwarding is technically the 
> same and you can achieve the same results with either though.  Personally, 
> I'm a fan of l2vpn the use of RSVP allows for more tidy configuration and 
> bandwidth reservations.  I think l2vpn is a little easier to troubleshoot 
> as well, however YMMV.

It should also be noted:

- Both methods require MPLS. In that respect neither of them can
replace an L2TPv3 based pseudowire, since L2TPv3 can ride on top of
standard IP.

- l2circuit is interoperable (for instance between Juniper and Cisco),
while l2vpn is not.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no