From: Skinner, Stephen (Stephen.Skinner@rbs.co.uk)
Date: Thu Jun 29 2006 - 04:43:25 ART
Brian ,
thank you for your response.
that has answered the question perfectly .
Thank you very much
Stephen
> -----Original Message-----
> From: Brian McGahan [SMTP:bmcgahan@internetworkexpert.com]
> Sent: 28 June 2006 17:54
> To: Skinner, Stephen; ccielab@groupstudy.com
> Subject: RE: IBGP v EBGP , quicker convergence
>
> *** WARNING : This message originates from the Internet ***
>
> Stephen,
>
> Per RFC 4271 the propagation delay for an advertisement should
> be based on how fast the device can process updates and run bestpath
> selection (function of cpu, memory, etc) and the
> "MinRouteAdvertisementIntervalTimer", which is similar to SPF delay in
> OSPF:
>
> <rfc>
> 9.2.1.1. Frequency of Route Advertisement
>
> The parameter MinRouteAdvertisementIntervalTimer determines the
> minimum amount of time that must elapse between an advertisement
> and/or withdrawal of routes to a particular destination by a BGP
> speaker to a peer. This rate limiting procedure applies on a per-
> destination basis, although the value of
> MinRouteAdvertisementIntervalTimer is set on a per BGP peer basis.
> </rfc>
>
> The notion that iBGP converges faster than EBGP is per the RFCs
> recommendation that:
>
> <rfc>
> Since fast convergence is needed within an autonomous system, either
> (a) the MinRouteAdvertisementIntervalTimer used for internal peers
> SHOULD be shorter than the MinRouteAdvertisementIntervalTimer used
> for external peers, or (b) the procedure describe in this section
> SHOULD NOT apply to routes sent to internal peers.
> </rfc>
>
> The problem is that you get into the meaning of SHOULD and
> SHOULD NOT as the RFC is just a recommendation, and the vendor doesn't
> necessarily have to follow it.
>
> In this particular case Cisco does implement this feature with
> the configurable timer "neighbor advertisement-interval"
>
> <CCO>
> neighbor advertisement-interval
> To set the minimum interval between the sending of Border Gateway
> Protocol (BGP) routing updates, use the neighbor advertisement-interval
> command in address family or router configuration mode. To remove an
> entry, use the no form of this command.
>
> Defaults
> 30 seconds for external peers and 5 seconds for internal peers.
> </CCO>
>
> The risk of changing this timer is that if you have rapid
> UPDATE/WITHDRAW messages and you propagate them to your EBGP peers you
> run the risk of having your prefixes dampened.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
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>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Skinner, Stephen
> > Sent: Wednesday, June 28, 2006 11:01 AM
> > To: 'ccielab@groupstudy.com'
> > Subject: IBGP v EBGP , quicker convergence
> >
> > guys,
> >
> > I have tried the CCO and I have tried the archive and have had no luck
> ,
> >
> > This is not a nice question , so I apologise in advance.
> >
> >
> > I have a BGP network and I want the fastest convergence (when a route
> is
> > missing) as possible. (WITHOUT modifying anything in BGP , just using
> the
> > defaults)
> >
> > can i first confirm a couple of things.
> > in a single BGP router.
> >
> > imagine full mesh. 1 route map to allow in networks
> >
> > 1.If i add a network to a route map , and nothing else
> > the BGP scanner will pick this up after a potential 60secs (depending
> on
> > the
> > timing cycle)
> > and then advertise it out to its peers (providing its allowed) yes ?
> >
> > i should not need to do a "clear ip BGP blah" command.
> >
> > 2.If a network goes missing , an update will be sent to BGP neighbours
> to
> > tell them about this.
> > this will only happen when the BGP scanner picks this up , which in
> theory
> > could be 60 seconds yes ?
> >
> >
> > the reason i ask is because of the following.
> >
> > i have been told that IBGP will converge faster than EBGP
> >
> > the reason for this is that a BGP command "update interval" which can
> > modify how often updates are sent.
> > and that by default an IBGP neighbour sends out an update every 5secs
> > .
> >
> > but for EBGP it sends it out every 30sec.
> >
> > so that would mean IBGP converges quicker than EBGP .
> >
> > i cant find this command on the CCO .
> >
> > also i believe this is in not related to convergence after a route is
> > lost.
> > but is related to how often standard updates are sent.
> >
> > i believe EVEN if there is such a command , when i loose a route ,
> BOTH
> > IBGP
> > and EBGP will send out a update (because triggered updates is on by
> > default)
> > at the same time,
> > therefore both IBGP and BGP will converge at the same time.
> >
> > am i wrong? , to be honest i don't know .
> >
> >
> > TIA
> >
> >
> > Stephen Skinner
> >
> >
> >
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