Re: BGP/OSPF router-id mismatch and the BGP synchronization

I do this mainly due to rule 2: It makes life easier administratively. :)

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Jared Scrivener
CCSI #30878, CCIE3 #16983 (R&S, SP, Security)
www.MicronicsTraining.com
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On Sat, Feb 13, 2010 at 2:46 PM, Divin Mathew John <divinjohn_at_gmail.com>wrote:
> Not a problem!
>
> HTH!
>
> On Sat, Feb 13, 2010 at 7:45 AM, Marcel Lammerse <m.lammerse_at_mac.com>
> wrote:
>
> > Thanks for your quick response Divin :) Just what I was looking for!
> >
> > Congratulations on passing your CCIE exam. You earned it mate.
> >
> >
> > On 13/02/2010, at 15:15 , Divin Mathew John wrote:
> >
> > > Check this out. http://www.internetworkexpert.com/rfc/rfc1403.txt
> > > 3.  BGP Identifier and OSPF router ID
> > >
> > >    The BGP identifier MUST be the same as the OSPF router id at all
> > >    times that the router is up.
> > >
> > >    This characteristic is required for two reasons.
> > >
> > >      i    Synchronisation between OSPF and BGP
> > >
> > >           Consider the scenario in which 3 ASBRs, RT1, RT2, and RT3,
> > >           belong to the same autonomous system.
> > >
> > >
> > >                                      +-----+
> > >                                      | RT3 |
> > >                                      +-----+
> > >                                         |
> > >
> > >                           Autonomous System running OSPF
> > >
> > >                                  /               \
> > >                              +-----+          +-----+
> > >                              | RT1 |          | RT2 |
> > >                              +-----+          +-----+
> > >
> > >
> > >           Both RT1 and RT2 have routes to an external network X and
> > >           import it into the OSPF routing domain.  RT3 is advertising
> > >           the route to network X to other external BGP speakers.  RT3
> > >
> > >
> > >
> > > Varadhan                                                        [Page
> 5]
> > >
> > > RFC 1403                  BGP OSPF Interaction              January
> 1993
> > >
> > >
> > >           must use the OSPF router ID to determine whether it is using
> > >           RT1 or RT2 to forward packets to network X and hence build
> the
> > >           correct AS_PATH to advertise to other external speakers.
> > >
> > >           More precisely, RT3 must determine which ASBR it is using to
> > >           reach network X by matching the OSPF router ID for its route
> > >           to network X with the BGP Identifier of one of the ASBRs, and
> > >           use the corresponding route for further advertisement to
> > >           external BGP peers.
> > >
> > >      ii   It will be convenient for the network administrator looking
> at
> > >           an ASBR to correlate different BGP and OSPF routes based on
> > >           the identifier.
> > >
> > >
> > > On Sat, Feb 13, 2010 at 6:16 AM, Marcel Lammerse <m.lammerse_at_mac.com>
> > wrote:
> > > Hi all,
> > >
> > > I know this is not common these days, as BGP synchronization is turned
> > off by default in recent ios versions. However, I was wondering if anyone
> > knows why a Cisco router considers an OSPF route not synchronized, if the
> > OSPF router id and BGP router id don't match.
> > >
> > > Is this an implementation-specfic thing or is there some protocol
> design
> > thinking behind it?
> > >
> > >
> > > Blogs and organic groups at http://www.ccie.net
> > >
> > > _______________________________________________________________________
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > --
> > >
> > > Sent from Doha, Qatar
> >
> >
>
>
> --
>
> Sent from Doha, Qatar
>
>
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>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
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>
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>
>
>
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>
-- 
Cheers,
Jared Scrivener
CCSI #30878, CCIE3 #16983 (R&S, SP, Security)
www.MicronicsTraining.com
Sr. Technical Instructor
YES! We take Cisco Learning Credits!
Training And Remote Racks available
LinkedIn:www.linkedin.com/in/jaredscrivener
Blogs and organic groups at http://www.ccie.net