Re: OSPF LSA TYPE 3 OVER BACKDOOR LINK

Output :-)

On Tue, Sep 24, 2013 at 3:45 PM, Tolulope Adeniji <toluadeniji_at_gmail.com>wrote:

> 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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> >
> >
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Received on Tue Sep 24 2013 - 16:38:05 ART