Re: Question about overlapping IP space and L3VPN central

 Hi John,

In the MPLS VPN routing model, the PE router provides isolation between
customers using VRFs. However, this information needs to be carried between
PE routers to enable data transfer between customer sites via the MPLS VPN
backbone. The PE router must be capable of implementing processes that
enable overlapping address spaces in connected customer networks. The PE
router must also learn these routes from attached customer networks and
propagate this information using the shared provider backbone. This is done
by the association of a route distinguisher (RD) per virtual routing table
on a PE router.

A RD is a 64-bit unique identifier that is prepended to the 32-bit customer
prefix or route learned from a CE router, which makes it a unique 96-bit
address that can be transported between the PE routers in the MPLS domain.
Thus, a unique RD is configured per VRF on the PE router. The resulting
address, which is 96-bits total (32-bit customer prefix + 64-bit unique
identifier or RD), is called a VPN version 4 (VPNv4) address.
VPNv4 addresses are exchanged between PE routers in the provider network in
addition to IPv4 (32-bit) addresses.

Further reading, you can go through very good books .. MPLS on Cisco IOS,
MPLS VPN Architectures 1 & 2 (both Cisco press books)

HTH

RR-

> On Mon, Jul 30, 2012 at 2:12 AM, John Neiberger <jneiberger_at_gmail.com
> >wrote:
>
> > I'm just now getting around to really studying L3VPN. I'm playing around
> > with GNS3 while watching some training videos and my latest little lab
> > setup involves configuring basic central services. For the sake of
> > discussion, imagine three VRFs: A, B and C, as well as a new VRF called
> > SERVICES. I have customers in these VRFs spread out across the network,
> and
> > they do use overlapping IP space. When I configured this in my lab with
> one
> > customer, I found (remember, I'm new to this!) that I had to import the
> > customer routes into the new SERVICES VRF, which makes sense. Without
> those
> > routes in the VRF, the router can't forward packets to those destinations
> > even if the correct routes exist in other VRFs on that router.
> >
> > But what happens when I import another customer into that table? Let's
> say
> > the VPN associated with VRF A is using 10/8 space, and so it the VPN
> > associated with VRF B. If I have already imported the routes for
> Customer A
> > into my Services VRF, how is this going to behave if I then import the
> > routes for Customer B using the same space? I realize that VPNv4 routes
> are
> > kept unique with the use of an RD. Does a PE router do something similar
> > when importing multiple sets of routes into a VRF? Does it retain the RD
> to
> > keep them unique somehow? If not, how do I handle having to import
> > overlapping prefixes to make central services work?
> >
> > Thanks!
> > John
> >
> >
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>
>
> --
> Best regards,
> Dan
>
>
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Received on Mon Jul 30 2012 - 09:57:18 ART