From: Peng Zheng (zpnist@yahoo.com)
Date: Tue Apr 08 2003 - 11:21:55 GMT-3
Thanks.
--- Ahmed Hassan <ahmed_hassan@rayatelecom.net> wrote:
>
> Peng Zheng,
> the router will prefer the Lower ID only if your two
> EBGP paths have the same time,
> So I think normally when you reload the router or
> clear The BGP table you will have one of the paths
> older that the other so the router will prefer the
> older Path (I think most of the time one of the
> neighbors will establish BGp session before the
> other).
> In Case Of IBGP the BGP will choose the Closest IBGP
> neighbor
> Best regards
> *************************************
> Ahmed Hassan
> Network Planning and configuration Engineer
> Raya Telecom
> ahmed_hassan@rayatelecom.net
> *************************************
> -----Original Message-----
> From: Peng Zheng [mailto:zpnist@yahoo.com]
> Sent: Monday, April 07, 2003 9:52 PM
> To: Jonathan V Hays; ccielab@groupstudy.com
> Subject: RE: Lowest BGP router ID prefered ?
>
>
> Thanks. Yesterday, it preferred 192.168.1.249 even
> after reloaded.
>
> I just tried today, it preferred 192.168.1.241. I
> don't know why.
>
>
>
> --- Jonathan V Hays <jhays@jtan.com> wrote:
> > Please verify the router IDs of those neighbors.
> > Note that the router ID
> > may not be the same as the Next Hop IP address.
> For
> > example, see below
> > where the next hop is 10.1.1.2 but the neighbor's
> > router ID is
> > 172.16.3.1.
> >
> > r2501a#show ip bgp neighbors
> > BGP neighbor is 10.1.1.2, remote AS 2, external
> > link
> > BGP version 4, remote router ID 172.16.3.1
> > BGP state = Established, up for 00:19:33
> > [output omitted]
> >
> >
> > > -----Original Message-----
> > > From: Peng Zheng [mailto:zpnist@yahoo.com]
> > > Sent: Monday, April 07, 2003 2:55 AM
> > > To: Jonathan V Hays; ccielab@groupstudy.com
> > > Subject: RE: Lowest BGP router ID prefered ?
> > >
> > >
> > > But I implemented the same topology as that.
> > > Sugarbush has three IP: 192.168.1.253 (to
> Stowe),
> > > 192.168.1.238 (to Diamond) and 192.168.1.249 (to
> > > Burke), so BGP ID is 192.168.1.253.
> > >
> > > And Diamond has three IPs too: 192.168.1.245 (to
> > > Mammoth), 192.168.1.237 (to Sugarbush) and
> > > 192.168.1.241 to Burke), so its BGP ID is
> > > 192.168.1.245.
> > >
> > > And I got the same route table on burke(
> preferred
> > > Sugarbush).
> > >
> > >
> > > --- Jonathan V Hays <jhays@jtan.com> wrote:
> > > > You are referring to BGP Best Path Selection:
> > > >
> > > >
> > >
> >
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios12
> > > 1/121cgcr/
> > > > ip_c/ipcprt2/1cdbgp.htm#1000898
> > > >
> > > > "12. If multipath is not enabled, prefer the
> > route
> > > > with the lowest IP
> > > > address value for the BGP router ID.
> > > > The router ID is usually the highest IP
> address
> > on
> > > > the router or the
> > > > loopback (virtual) address, but might be
> > implementation-specific. "
> > > >
> > > > I think you are mistaken on the IP addresses
> you
> > > > gave since I don't see
> > > > either 192.168.1.253 or 192.168.1.245 on page
> > 191 of
> > > > that book. Perhaps
> > > > I have a different printing than you do.
> Anyway,
> > I
> > > > assume you are
> > > > referring to Example 2-53 "Burke's BGP Table
> > > > Contains Only the Aggregate
> > > > Route" which shows 192.168.1.249 as having the
> > best
> > > > path instead of
> > > > 192.168.1.241 (the lower IP address).
> > > >
> > > > Although the BGP router chosen as the Next Hop
> > for
> > > > this network happens
> > > > to have the higher IP address value, you do
> not
> > have
> > > > enough information
> > > > to say that it was the IP address value used
> by
> > BGP
> > > > to make that
> > > > decision. There are eleven (11) previous steps
> > in
> > > > the BGP Best Path
> > > > Selection hierarchy, any one of which takes
> > > > precedence over this IP
> > > > address criteria. The IP address criteria
> won't
> > be
> > > > used unless all of
> > > > the other criteria are bypassed or are equal
> for
> > > > both routers.
> > > >
> > > > Hope that helps.
> > > >
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: nobody@groupstudy.com
> > > > [mailto:nobody@groupstudy.com] On
> > > > > Behalf Of Peng Zheng
> > > > > Sent: Sunday, April 06, 2003 10:21 PM
> > > > > To: ccielab@groupstudy.com
> > > > > Subject: Lowest BGP router ID prefered ?
> > > > >
> > > > >
> > > > > Hi,
> > > > >
> > > > > It is said the route with lowest BGP router
> ID
> > is
> > > > > preferred. But I found the route with
> > highest
> > > > BGP
> > > > > router ID os preferred.
> > > > >
> > > > > In Route TCP/IP V2, page 191, on Burke, the
> > route
> > > > with
> > > > > BGP ID 192.168.1.253 is preferred to the
> route
> > > > with
> > > > > BGP ID 192.168.1.245.
> > > > >
> > > > > What's the reason?
> > > > >
> > > > > Thanks for help.
> > > > >
> > > > >
> > > > >
> > > > >
> > __________________________________________________
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>
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