From: jonatale@xxxxxxxxxxxxx
Date: Sat Feb 16 2002 - 15:43:01 GMT-3
yup, there it is:
"
The BGP identifier MUST be the same as the OSPF router id at all
times that the router is up."
I'd say it is a Cisco non-compiance; but then again, I'd say the king was
naked...
:-)
Brian Dennis wrote:
> John,
> Are you referring to RFC 1403?
>
> http://www.faqs.org/rfcs/rfc1403.html
>
> Brian Dennis, CCIE #2210 (R&S)(ISP/Dial) CCSI #98640
> 5G Networks, Inc.
> brian@5g.net
>
> >From RFC 1403
>
> 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
>
> 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.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> John Neiberger
> Sent: Tuesday, January 15, 2002 7:44 AM
> To: j killion; ccielab@groupstudy.com
> Subject: Re: RE: BGP "no sync"
>
> It's documented in an RFC, but I can't remember which one.
> This requirement has been obsoleted by a new RFC but Cisco
> hasn't changed the behavior.
>
> Take the following example:
>
> [A]---(ospf)-----[B]----(ospf)----[C]
> \--------------(ibgp)-------------/
>
> A and C are iBGP peers. C has an external BGP connection and
> it's redistributing eBGP into OSPF. It then advertises those
> same routes via iBGP to A.
>
> A learns these prefixes via OSPF from B and via iBGP from C.
> There is your mismatch. If you were to do a 'show ip bgp
> a.b.c.d' on one of those routes it would show as not
> synchronized even though you'd think it would be.
>
> You can tweak either the OSPF router ID on B or the BGP router
> ID on C. You have to be careful when you do this but it's one
> way to fix the problem, depending on your topology.
>
> HTH,
> John
>
This archive was generated by hypermail 2.1.4 : Thu Jun 20 2002 - 13:46:25 GMT-3