Giuseppe Larosa Sun, 11/23/2008 - 02:38
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Hello James,

VPLS is thought to run over an MPLS/IPv4 core.

I don't think it can run over an IPv4 only core.


You can provide L2 transport services over an IPv4 only network using L2TPv3, but I think they are point-to-point only services like EoMPLS point-to-point service.


Hope to help

Giuseppe


marikakis Sun, 11/23/2008 - 14:39
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Hello,


I almost agree with Guiseppe. I am under the impression that Virtual Private LAN Service (VPLS) is a service (as its name also states) more general than the specific technology actually used to implement it. Of course, what you can actually do in a network depends on the actual implementation.


RFC 4762 (VPLS Using LDP Signaling) shows the topological model for VPLS: http://tools.ietf.org/html/rfc4762#section-4

While commenting on the cloud shown in the topology, the authors say: "We note here again that while this document shows specific examples using MPLS transport tunnels, other tunnels that can be used by PWs (as mentioned in [RFC4447]) -- e.g., GRE, L2TP, IPsec -- can also be used, as long as the originating PE can be identified, since this is used in the MAC learning process."


Another service popping up is IP-Only LAN Service (IPLS), described in a draft (short description of IPLS is found in the introductory Abstract section). IPLS topology diagram can be seen at:

http://tools.ietf.org/html/draft-ietf-l2vpn-ipls-08#section-3.0

The comment of the authors in this case is: "PE1, PE2 and PE3 are shown as connected via an MPLS network; however, other tunneling technologies, such as GRE, L2TPv3, etc., could also be used to carry the pseudowires."


As for the point-to-point versus point-to-multipoint comparison, I am not so sure. I mean, the VPLS configuration that I am aware of seems to me very similar to a full-mesh of point-to-point AToM VCs (you say "neighbor" instead of "xconnect" to LDP peer). It could easily be that the MPLS logic underneath builds the related LSPs in a point-to-point fashion. I think those are all emulations and as such their purpose is to give us an illusion (which can easily turn out to be not a very good one). People keep trying to emulate Ethernet LAN behavior over other types of media (has been tried in ATM too). They are destined to replicate broadcast and multicast packets across VCs or pseudowires or anything.


It seems to me that there is a tendency towards pure IP networks. I've been reading that MPLS can be used as a migration path into next-generation metro provider services (IP/VPNs). And I suspect they are going to tell us at some point that MPLS is a "legacy" technology!


Kind Regards,

M.

jiaqyu Mon, 11/24/2008 - 21:08
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Yes, VPLS will work over IP backbone as long as MPLS is supported.

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