Re: OSPF LSA TYPE 3 OVER BACKDOOR LINK

Thanks Brian. Quite aware of the down bit but this is not a VRF lite CE. I
was actually working on INE SP lab 4.12 (MPLS L3 VPN and OSPF Domain-ID)
but modified the backdoor link area to be in AREA 0 while every other thing
remain same.

Also i don't think Sham link would help out here b'cos the original route
is advertised into OSPF as OIA routes (i.e the loopback 0 on R1 and XR2).

Would appreciate further inputs on this.

On Tue, Sep 24, 2013 at 9:12 PM, Brian Dennis <bdennis_at_ine.com> wrote:

> If the CE's OSPF process is within a VRF then it will check for the down
> bit on type 3 LSAs as a loop prevention mechanism (see the first link below
> for more detail). If the PE is setting the down bit (this happens when
> MBGP is redistributed into the PE-CE OSPF process for type 3 LSAs the PE
> generates) then the CE will not use the type 3 LSA that has the down bit
> set by default. If you want the CE to ignore the down bit and use the type
> 3 LSA from the PE that has the down bit set, then the capability vrf-lite
> command under the OSPF VRF process on the CE should be enabled.
>
> A SHAM link will also resolve the issue. With a SHAM link from PE to PE
> across the MPLS VPN the down bit will not be set by the PEs any longer for
> the type 3 LSAs since the loop prevention mechanisms of the down bit and
> domain tag are not needed any longer when a SHAM link is used.
>
> Inter-Area Loop Prevention in OSPF
> http://ine.co/0yauq
>
> Configuring VRF-lite - Cisco
>
> http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/25ew/configuration/guide/vrf.html
>
> --
> Brian Dennis, CCIEx5 #2210 (R&S/ISP-Dial/Security/SP/Voice)bdennis_at_ine.com
>
> INE, Inc. http://www.INE.com
>
>
>
> On 09/24/2013 08:00 AM, Tolulope Adeniji wrote:
>
> Hello
>
> Why would a CE prefer a OSPF type 3 lsa learnt over backdoor link to same
> type 3 lsa advertised by connecting PE despite the higher metric across the
> backdoor link.
>
> Regards
>
>
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Received on Tue Sep 24 2013 - 23:45:57 ART