The MPLS-OPS Archive

[Daniel Kharitonov <dkharitonov@yahoo.com>]

> Which is one of the reasons why L2 VPNs over MPLS
> are getting much attention.

L2 VPNs are a good solution to one problem and a bad
solution to another. Specificly, "fixing" the need for
the usable L3 VPNs w/L2 VPNs is a bad trend.
First, L2 VPN needs n^2/2 tunnels to be configured for
n customer endpoints. Next, hauling full L2 (read,
Ethernet) traffic is unnecessary and also brings the
MTU problem on the table. You will be very surprised
to know, how many brand-name routers and switches are
simply incapable of taking ethernet packets larger
than 1536 bytes.
In a word, I am a strong advocate for the L3 VPNs
without client's routing tables propagated through
ISP.
For me, the service model should look like this: you
just give the client IP connectivity between his edge
routers, the client extends his IGP/EGP over this
structure. Again, the only problem is that current
IGPs do not have the notion of the "multihop"
connections.

> >  Second, the lack of multicast supports prevents
> >deploying MPLS in MANs.
> 
> Care to elaborate on why you believe it's
> impossible?

It is, indeed, possible. As I said, early tag
switching implementations even suggested this.
However, later the development of multicast over
tags/MPLS have been stopped in favor of the more "host
topics". Currently no vendors support multicast over
MPLS.

--
DK

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