The MPLS WG Archive

[Robert Raszuk <raszuk@cisco.com>]

Arun,

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

I would ask an opposite question:

Please indicate one advantage of turning your directed LDP into IBGP ???

[Just don't say an obvious one - that some vendors don't know how to
write a bgp code.]

R.

> Arun Kumar Dheena wrote:
> 
> 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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