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Re: OT: how to filter out several VPNs from a MPLS backbone backup path posted 03/24/2006
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On Fri, Mar 24, 2006 at 12:50:28PM +0200, sheherezada@xxxxxxxxx wrote:
> Hi all,
> I have four routers linked in a row, let's say A-B-C-D, and a lower
> bandwidth backup link between A and D. I have just added MPLS and set
> up several VPNs, but I don't want all VPNs to generate traffic on the
> backup link when it comes up. Any idea of how to do it?
> Thanks,
> Mihai

Hi Mihai,

here is a possible solution. I have put also the CCIE SP list on CC
since this is more a topic for there...

- create a second loopback interface on the pe-routers.

- add your second loopback interface into your igp so it is reachable

- filter your LDP so it is not assigning and distributing any labels
for this second loopback

- change the next-hop ip-address that bgp will advertise for the 
  VPN that you do not want to have on the low-bandwidth backup link

  Example> Assuming Lo1 is the Loopback where you are not distributing labels
 ip vrf TWO
 rd 2:1
 route-target export 2:1
 route-target import 2:1
 bgp next-hop Loopback1

- at this point this VPN will not work anymore, because you have no 
  LSP to the new Loopbacks 

- enable MPLS Traffic Engineering, use the new loopback ip as router-id
  for mpls traffic engineering

- build mpls-te tunnels between the new loopback addresses. Use an
  explicit path that excludes the ip addresses of the low-bandwidth
  backup link.

- at this point the VPN will work again. LSPs are provided through 
  MPLS-TE. As soon as the main link between your PE routers goes
  down the MPLS-TE Tunnel will also go down because they are not 
  allowed to signal a path through your low-bandwidth link.

hope the explanation is not too confusing.