From: Carlos (cchorao@xtra.co.nz)
Date: Sat Jan 04 2003 - 02:26:23 GMT-3
I agree, and in my opinion the statement on the top of page 48 (BGP-4
command and config ) is an error.
Carlos
Telecom New Zealand - Advanced Solutions Group : Network Design and Security
----- Original Message -----
From: "cebuano" <cebu2ccie@cox.net>
To: <ccielab@groupstudy.com>
Sent: Saturday, January 04, 2003 4:04 AM
Subject: RE: Clarification needed on BGP and MEDs
> Well, if you haven't noticed yet, the Parkhurst book you are referring
> to has MANY, MANY technical info NOT included, specially since it was
> written pre-12.2 and does not present the topic from an ISSUES
> perspective but simply to test the different commands. Don't forget to
> also check its errata on Ciscopress because I've exchanged e-mails with
> the author to confirm the errors I found both in this book and the OSPF
> command reference book as well.
>
> Regards.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Jennifer Bellucci
> Sent: Friday, January 03, 2003 1:38 AM
> To: cebuano; ccielab@groupstudy.com
> Subject: Re: Clarification needed on BGP and MEDs
>
> get hold of BGP config and command handbook from ciscopress. Did wonders
> for
> me, after that flick through halabi and JD 2, those books are good for
> the
> concepts and stuff but the book above gives you what I wanted, to find
> out
> what all the commands actually do, plus reading the command guide can
> sometimes damage your mental stability.
> ----- Original Message -----
> From: "cebuano" <cebu2ccie@cox.net>
> To: <ccielab@groupstudy.com>
> Sent: Friday, January 03, 2003 5:46 AM
> Subject: Clarification needed on BGP and MEDs
>
>
> > Hi group.
> > I need to clarify my reading of this CCO page.
> >
> > The following examples demonstrate how the bgp deterministic med and
> bgp
> > always-compare-med commands can influence MED-based path selection.
> > Note: Cisco Systems recommends enabling the bgp deterministic med
> > command in all new network rollouts. For existing networks, the
> command
> > must either be deployed on all routers at the same time, or
> > incrementally, with care to avoid possible internal BGP (iBGP) routing
> > loops.
> > For example, consider the following routes for network 10.0.0.0/8:
> > entry1: AS(PATH) 500, med 150, external, rid 172.16.13.1
> > entry2: AS(PATH) 100, med 200, external, rid 1.1.1.1
> > entry3: AS(PATH) 500, med 100, internal, rid 172.16.8.4
> > The order in which the BGP routes were received is entry3, entry2, and
> > entry1 (entry3 is the oldest entry in the BGP table and entry1 is the
> > newest one).
> > Note: When BGP receives multiple routes to a particular destination,
> it
> > lists them in the reverse order they were received, from the newest to
> > the oldest. BGP then compares the routes in pairs starting with the
> > newest entry and moving toward the oldest entry (starting at top of
> the
> > list and moving down). For example, entry1 and entry2 are compared.
> The
> > best of these two is then compared to entry3, and so on.
> >
> > Example 1: Both Commands Disabled
> >
> > Entry1 and entry2 are compared first. Entry2 is chosen as the best of
> > these two because it has a lower router ID. The MED is not checked
> since
> > the paths are from a different neighbor AS.
> > Shouldn't example 1 instead say, "Entry2 is chosen as the best of
> these
> > two because it has an OLDER received path"?
> > Step 10 of the BGP Bestpath Selection states.
> > "When both paths are EXTERNAL, prefer the OLDEST path."
> > Isn't Entry2 "older" than Entry1?
> > Or is something wrong with my understanding of this English?
> >
> > TIA.
> > Elmer
> >
> > BTW - do you guys/gals have a recommendation on very good lab
> scenarios
> > to bring the true IOS behavior of these different BGP "knobs" to life?
> > There are so many changes to the 12.2 release that it makes me not
> want
> > to dwell too much on Halabi's book. I wish Doyle had THREE chapters on
> > this instead of two (pity he spent three chapters on Multicast
> instead).
> > .
> .
> .
.
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