From: Ian Blaney (ian.blaney@gmail.com)
Date: Wed Jul 18 2007 - 10:21:54 ART
Samarth
Thanks for your answer.
Its not that I want to see intra-area routes I am just wondering why by
default they are inter-area. As far as I understand sham links are used in
the special case where you have a backdoor link between 2 sites. Without the
sham link, the backdoor link would be preferred over the SP core ie intra
preferred over inter routes, however, this would not be scalable with a VPN
with many sites if you wanted to use it for the purpose of seeing just
intra-area routes.
As you say the down bit for inter-area routes and domain-tag for external
routes is used to prevent loops ie a route advertised by a PE into a OSPF
area will not be advertised by another PE in the same area back into the SP
Core. Why can the same concept not be used for internal routes advertised by
the egress PE router into the OSPF area?
Cheers
Ian Blaney
On 7/18/07, sam s <samarth_04@hotmail.com> wrote:
>
> Hi,
>
> You can use Shamlinks if you want to see intra-area(o) routes.
> The reason I think you would see inter-area routes (IA) is to prevent
> loops, as down bit is set for them.
>
>
> Best Wishes,
> SAMARTH
>
>
>
> > Date: Wed, 18 Jul 2007 14:40:10 +0200
> > From: ian.blaney@gmail.com
> > To: ccielab@groupstudy.com
> > Subject: MPLS VPN - OSPF PE-CE
> >
> > Hello All
> >
> > I have a SP related question which hopefully someone can help me with.
> >
> > In a Layer 3 MPLS VPN where OSPF is used as the PE-CE routing protocol
> why
> > are all internal routes from one site sent as inter-area routes to
> another
> > site? I understand the concept that the SP core acts as the super
> backbone
> > and the PEs are ABRs instead of ASBRs which would normally be the case
> when
> > redistributing from one protocol to the other ie OSPF <-> MP-BGP.
> >
> > Surely the SP core should be as transparent as possible. The OSPF
> network
> > type is sent in the extended communities attribute so it wouldn't be
> > difficult for the egress PE to reconstruct the original OSPF internal
> route.
> >
> >
> > Am I misunderstanding something here?
> >
> > Regards
> > Ian Blaney
> >
> > _______________________________________________________________________
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