The MPLS WG Archive

["Arun Kumar Dheena" <arunkumar.dheena@wipro.com>]

Hi,
       Thanks for your replies.

The draft-martini-l2circuit, does establish point-to-point tunnel between
PE-LSR's. It maps the incoming L2 traffic onto the corresponding
point-to-point tunnel.

Suppose, if we establish direct LDP session between PE-LSRs as in
martini-drafts  but instead of  exchanging L2 information (as in L2VPNs) we
exchange L3 VPN related information as in BGP/MPLS VPN (by defining
RouteTarget-TLV, VPN-Label, VPN-IPv4 TLV to the LDP etc), we (might) get a
Layer 3 VPN without using BGP.  With filtering capabilities, LDP-VPN can
support the features as in BGP/MPLS VPNs. The PE-LSR - CE routing has to be
explored in this approach.

 What are the flaws/disadvantages in this approach. Is this worthwhile?

As Miquel has mentioned, the PE-LSR's has to be fully-meshed but only in the
"worst case" (because,  a PE-LSR will establish a LDP session with another
PE-LSR only if they have a VPN-site in common). Yes, this is a limitation
but then there is no FEC reflector(!) concept in LDP.


Thanks in Advance

regards
arun



> > Hi,
> >       The RFC 2547bis uses BGP to distribute the VPN routes.
> > But, we can
> > modify LDP itself to carry the information carried in BGP like the VPN
> > routes, route targets and VPN labels etc (by defining, new
> > TLVs and new LDP
> > messages).
> >
>
> LDP distributes LABELS bindings to FECs, those being IPv4, VPNv4,
> MAC addresses, VC's or whatever else. Imagine a situation where
> PEs are separated by LSR routers that do not have any notion of
> the FEC for which you are binding the label. Since they don't
> understand the FEC, they can not give you a label binding. This
> is why LDP directed sessions are used for anything else than
> IPv4 (for example, Martini). Either that or you have to do all
> the LSR in the path "aware" of the FEC. The idea of MP-BGP is
> pretty much the same, you are using BGP sessions between all the
> peers to exchange VPNv4 information.
>
>
> > The motivation for this is, firstly, the LDP-VPNs can provide the same
> > scalability as in mentioned RFC2547, as the intermediate
> > LSR's (P routers)
> > need not maintain the VPN-Lables and routes. (This can be achieved by
> > maintaining LDP sessions between the PE LSR's). Secondly, we
> > can avoid using
> > BGP for MPLS-VPNs.
>
> Sure you can, but in this case remember you will have to maintain
> a LDP session for each of the PEs (full mesh) I'd like to see you
> maintaining a couple hundreds PEs with full meshing requirements,
> without all the handy mechanisms BGP has (for example, Route Reflectors)
> Or maybe we can add the notion of Route Reflectors to LDP...
>
> >
> > Will this apparach be an alternate for BGP/MPLS VPN?
> > Or am I missing something  fundamental?
> > I want to know whether any work has been done in this direction.
> >
>
> Ask the folks at PPVPN
>
>
> > Thanks in advance.
> > regards
> > arun
> >
> > Wipro-CDC
> >
> >
> >
> >
> >
> >
>

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