From: wing_lam@jossynergy.com
Date: Mon Jun 09 2003 - 12:28:27 GMT-3
Dear Snow,
To summarize:
BGP always compare med: compare MED between different ASs including
confederation external
BGP deterministic med: choose a best path according to MED among several
paths from each AS first.
BGP bestpath med-confed: compare MED only for confederation external, but
not external ASs
Am I right?
Thx,
BBD (Big Black Dog)
"Snow, Tim"
<timothy.snow@eds To: "'wing_lam@jossynergy.com'" <wing_lam@jossynergy.com>
.com> cc: "'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
Sent by: Subject: RE: Confederation
nobody@groupstudy
.com
06/09/2003 12:41
PM
Please respond to
"Snow, Tim"
Step 6
This comparison is only done if the first (neighboring) AS is the same in
the two paths; any confederation sub-ASs are ignored. In other words, MEDs
are compared only if the first AS in the AS_SEQUENCE is the same for
multiple paths. Any preceding AS_CONFED_SEQUENCE is ignored.
If bgp bestpath med-confed is enabled, MEDs are compared for all paths that
consist only of AS_CONFED_SEQUENCE (paths originated within the local
confederation).
In your email, I don't see any confederation AS #'s listed in the bgp
path...
Can you draw up the topology ?
http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuratio
n_guide_chapter09186a00800d97fc.html#1002381
Tim
-----Original Message-----
From: wing_lam@jossynergy.com [mailto:wing_lam@jossynergy.com]
Sent: Monday, June 09, 2003 12:36 AM
To: Snow, Tim
Cc: 'ccielab@groupstudy.com'
Subject: RE: Confederation
Thanks Tim,
Thanks, I can see that the following link shows confed external and
internal doesn't make the different:
http://www.cisco.com/en/US/tech/tk365/tk80/technologies_tech_note09186a00800
94431.shtml
Now I am really confused as I found in several books that confed external
will take preference than confed internal, like Internet Routing
Architectures - p.168.
Am I wrong in concept? Or I should trust the WEB?
Thx,
BBD (Big Black Dog)
"Snow, Tim"
<timothy.snow@eds To:
"'wing_lam@jossynergy.com'" <wing_lam@jossynergy.com>
.com> cc:
"'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
Subject: RE: Confederation
06/09/2003 12:12
PM
try med-confed...
Once thing I noticed is that you have a "confed-internal" and a
"confed-external".
Turn on always-compare-med and med-confed for comparing med's between
confederation peers.
Tim
-----Original Message-----
From: wing_lam@jossynergy.com [mailto:wing_lam@jossynergy.com]
Sent: Sunday, June 08, 2003 10:07 PM
To: Howard C. Berkowitz
Cc: ccielab@groupstudy.com
Subject: Re: Confederation
Thanks Howard,
No matter I activated "bgp detereministic-med" it still choose the
confed-internal route, as shown as following:
R8#sh ip b 10.26.1.0
BGP routing table entry for 10.26.1.0/24, version 11
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
172.16.1.26
(26)
172.16.1.26 (metric 97) from 172.16.1.5 (172.16.1.5)
Origin IGP, metric 0, localpref 100, valid, confed-internal, best
(26)
172.16.1.26 (metric 97) from 172.16.1.26 (172.16.1.26)
Origin IGP, metric 0, localpref 100, valid, confed-external
Thx,
BBD (Big Black Dog)
"Howard C.
Berkowitz" To:
ccielab@groupstudy.com
<hcb@gettcomm.com cc:
> Subject: Re: Confederation
Sent by:
nobody@groupstudy
.com
06/09/2003 12:38
AM
Please respond to
"Howard C.
Berkowitz"
At 7:57 PM +0800 6/8/03, wing_lam@jossynergy.com wrote:
>Hi, Group,
>
>According to theory, BGP will choose external router rather than
>confederation external, and confederation external will take preference
>than internal, when all other BGP attributes are the same. But in my own
>lab, I tested that it's not true and BGP will choose the lower metric (if
>metric not the same), even it won't regard whether it's BGP external or
>confederation external (if metric the same, it choose lower router ID).
>Just want to ask whether someboday has the same experience or it just a
bud
>in my IOS image. (I have tested several scenarios and gives the same
>result)
Do you have BGP deterministic-med coded on the interfaces in
question? It often clears obscure problems like this.
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