The MPLS-OPS Archive

[sthaug@nethelp.no]

> What would be the minimum bitrate and what access technology, for
> which it would make economic sense to deploy VPLS?  (as opposed to,
> for instance, having more "traditional" L3 VPNs such as BGP/MPLS or
> Virtual Router)

I'm still not sure that's the right question. L2 VPNs (VPLS) and L3
VPNs (MPLS/RFC 2547 or similar) serve different purposes. Both are
point to multipoint technologies, so they can basically handle much
the same topologies. 

L3VPNs:
- Have no issues with MAC learning, spanning tree protocol and similar.
- Nice if you want the ISP do to routing for you.
- You need to worry about routing protocol redistribution between BGP
(ISP) and customer routing protocols. Can strongly influence failover
times.
- More mature technology than L2VPNs.
- IP only.

L2VPNs:
- You need to worry about MAC learning, spanning tree protocol and
similar. Can strongly influence failover times (particularly with
traditional 802.1d).
- Nice if you want to do the routing yourself.
- No issues with routing protocol redistribution.
- Newer technology than L3VPNs, less equipment/fewer vendors that
support it.
- Protocol independent.

In some ways L2VPNs are "simpler" - but in reality this is only the
case if you're familiar with L2 networks and their issues.

Yes, there are time-sensitive L2 protocols (e.g. LAT, various IBM
protocols) that may need a higher bandwidth (say more than 256 kbps)
to work well over an L2 cloud. However, I would probably worry less
about that than the other points in the lists above - remember that
people have been running L2 protocols over low-speed FR links for
many years.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no

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