From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Tue May 11 2004 - 17:26:41 GMT-3
At 3:47 PM -0400 5/11/04, MMoniz wrote:
>Richard, I wouldn't take that to mean that you should be able to look up
>everything and be able to pass.
>
>But some things are just not going to come into play in the lab. Knowing how
>to find things will.
>
>Just like this topic. So you spend time trying to remember exactly the BGP
>route selection process.
>Then you get to the lab and they say something like rtr x should prefer this
>route without using
>As path, BGP router id , med or local pref. Since these things are so
>jumbled in the selction process
>chances are you are going to have to look this up any how. Thus you just
>wasted, well in my case, precious
>brain cell space on something that you no longer need to rememeber.
>
>Unless you have a photographic memory, or at least a bunch of unused brain
>cells to store this info, you are much
>better off knowing the core stuff and KNOWING where to find things on the
>doc CD/site that are a little abstract.
>
>Just my opinion,
>
>Mike
Let me offer my opinion as someone who has worked on BGP
implementation code and measurement standards. (with no false
modesty, take a look at
http://www.ietf.org/internet-drafts/draft-ietf-bmwg-conterm-05.txt,
which has been approved as an RFC as soon as we make some minor
changes in wording -- just clarifications). You can also find some
of my tutorials at my anonymous FTP server at www.netcases.net (FTP,
not HTTP), and, of course, I'll recommend my book, _Building Service
Provider Networks_.
In those cases, or in ISP operations, I rarely if ever needed to
remember EVERY decision rule. Some are just not used in practice.
Incidentally, a good aid to learning BGP is to make a table of the
attributes, ,mark them as eBGP-only vs. iBGP-only [0] vs. both, and
then note IF they are part of the route selection algorithm.
What really helped me understand BGP was going to the Routing Policy
Specification Language and predecessor documents, which explain the
problem the protocol is trying to solve. http://www.radb.net is a
good place to start looking for tutorials, as well as some RFCs and
the NANOG archives.
One needs to know both the generally accepted industry practice and
the knobs by which Cisco can vary the selection rules. RFC1771 is
sadly out of date. Use
http://www.ietf.org/internet-drafts/draft-ietf-idr-bgp4-23.txt as the
most definitive IETF document, which is both more accurate and better
written. You may want to go to the IETF IDR page,
http://www.ietf.org/html.charters/idr-charter.html, which has all the
RFCs and drafts, as there are some special cases in route selection,
such as confederation-external vs. true external (which also shows up
in the communities latest version).
[0] Some implementations do support what I'll call weird applications, such
as including LOCAL_PREF in eBGP updates. Personally, I think this is
crazy. The new BGP draft doesn't forbid it, though.
>
>
>
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
>Richard Dumoulin
>Sent: Tuesday, May 11, 2004 3:30 PM
>To: Andaluz, Danilo; swm@emanon.com; ccielab@groupstudy.com
>Subject: RE: BGP route selection
>
>
>Ok, but then everything is on the doc-cd ...
>
>-----Original Message-----
>From: Andaluz, Danilo [mailto:danny.andaluz@hp.com]
>Sent: martes, 11 de mayo de 2004 20:10
>To: swm@emanon.com; Richard Dumoulin; ccielab@groupstudy.com
>Subject: RE: BGP route selection
>
>
>I agree. Why remember it if it is out on the CD already?
>
>Danny
>
>-----Original Message-----
>From: Scott Morris [mailto:swm@emanon.com]
>Sent: Tuesday, May 11, 2004 1:26 PM
>To: 'Richard Dumoulin'; Andaluz, Danilo; ccielab@groupstudy.com
>Subject: RE: BGP route selection
>
>If you know where to look it up swiftly, you don't need ot know it by heart.
>
>There are too many things out there to try to memorize everything. Know the
>important things, don't sweat the details, but know how to find them!
>
>
>Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
>JNCIP, et al. IPExpert CCIE Program Manager IPExpert Sr. Technical
>Instructor swm@emanon.com/smorris@ipexpert.net
>http://www.ipexpert.net
>
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Richard Dumoulin
>Sent: Tuesday, May 11, 2004 1:15 PM
>To: Andaluz, Danilo; ccielab@groupstudy.com
>Subject: RE: BGP route selection
>
>Thx Danilo but I said "remember". How do you remember it ? By heart ?
>
>-----Original Message-----
>From: Andaluz, Danilo [mailto:danny.andaluz@hp.com]
>Sent: martes, 11 de mayo de 2004 19:09
>To: Richard Dumoulin; ccielab@groupstudy.com
>Subject: RE: BGP route selection
>
>
>
>http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
>fipr_c/ipcprt2/1cfbgp.htm#wp1000898
>
>Danny
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Richard Dumoulin
>Sent: Tuesday, May 11, 2004 12:59 PM
>To: ccielab@groupstudy.com
>Subject: BGP route selection
>
>Hello group,
>
> I am interested in how do you guys remember the bgp route slection
>algorythm ? Have you read so much BGP that it comes naturally ?
>
>Thank you
>
>--Richard
>
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