The MPLS WG Archive

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

Rafal,

> Yes, You miss few things.
>
> LDP is NOT routing protocol, so LDP cant populete VRF tables!
>

The basic idea of LDP-VPN is to form VPNs as in (similar to) BGP/MPLS VPN
without using BGP. The LDP needs to be extended with additional TLV's and
messages for this.  Please correct me if I am wrong with this approach.

In LDP-VPN we create per-site-NHLFE (VPN) and NOT  VRF's. The LDP is used to
populate the per-site-NHLFE (VPN) at the PE-LSR's.  This is done by LDP-VPN.
This is just an idea. We don't need routing to create VPN's.

> LDP run behind of IGP, but there are no IGP which may carry information
about overlaping IP addresses (like BGP do by VPN-IPv4 NLRI). To use LDP you
must develop IGP protocol. for OSPF it mean work from skrech. For IS-IS it
is a little bit easier (IS-IS have also TLVs) Theoretically, it is possible
to create something like VPN-IP v4 addrss family under IGP, but why do this
when we have provent protocol - BGP.
>

By adding new TVL's (for eg., VPN-IPv4-TLV) in LDP, the LDP carries the
VPN-IPv4 address. Thus it is possible to have over-lapping address space.
Similarly,  we should add Community TLVs.   The routing between the PE-LSR
and CE router needs to be explored.

> When We use BGP we have ext. community to limit connectivity in VPM and
for for example HUB-and-SPOK topology, Central Services Topology. Generally
You cant provide overlaping VPN. Theoretically, it is possible to create
something like community under LDP, but why do this when we have provent
protocol - BGP.
>
> Additionally, BGP gives possibility to create Interprovidr VPN. LDP domain
is limited to one ISP because LDP must run in connection with IGP.
>

True. It may not be possible.

> Furthermore BGP is designed for realy large scale (in mean of number of
routes) - other protocols not.
>
>
> I suggest you to read RFC2547bis but also
draft-martini-l2circut-trans-mpls (this use LDP for L2 VPN information
propagation), and draft-kompella-ppvpn-l2vpn (this use BGP similiar to
rfc2547bis)
>
>
> Rafal Jan Szarecki
> Senior System Engineer
> ATM/IP Backbone Network
> Ericsson Poland
> Product and Solution Department (EPO/S)
> *rafal.szarecki@epo.Ericsson.se
> *rafal.szarecki@Ericsson.pl
> *+48 602 418971
> '+48 22 6916635
>
>
> > -----Original Message-----
> > From: Arun Kumar Dheena [mailto:arunkumar.dheena@wipro.com]
> > Sent: Friday, February 22, 2002 1:08 PM
> > To: mpls@UU.NET
> > Subject: LDP - VPN
> >
> >
> > 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).
> >
> > 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.
> >
> > 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.
> >
> > Thanks in advance.
> > regards
> > arun
> >
> > Wipro-CDC
> >
> >
> >
> >
> >
> >

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