[c-nsp] bgp bestpath w/o bgp always-compare-med

[Vitkovsky, Adam]

Hi,
By default the MED comparison only occurs in the first (the neighboring) AS is the same in the two paths -which is not your case

Since these are eBGP routes the next tie breaker is:
Prefer the path that was received first (the oldest one)

IOS always displays the routes the way that the oldest one is at the bottom and the newest one is at the top of the "show ip bgp" output

So in your example the bottom one selected as the best is indeed the oldest one

I have this one printed out and always handy:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml


adam

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Nikolay Shopik
Sent: Tuesday, October 11, 2011 11:18 AM
To: cisco-nsp
Subject: [c-nsp] bgp bestpath w/o bgp always-compare-med

Hi,

I have rather strange best path selection. We have 3 uplinks, AS_PATH to 
one of prefix is same for all 3 prefixes, so my assumption it will use 
oldest one, because everything else is same. Except one thing I notice 
one of uplinks send us metric, while two others does not.

Here is example, first one is oldest, second is youngest, but it still 
choices last one. While should choice first, because everything else is 
same.

   39792 9002 25532
       Origin IGP, metric 400, localpref 100, valid, external
       Community: 39792:3000 39792:3004
   41095 9002 25532
       Origin IGP, localpref 100, valid, external
       Community: 41095:2000 41095:2001 41095:2100 41095:2101
   30733 9002 25532
       Origin IGP, localpref 100, valid, external, best
       Community: 9002:0 9002:64667 30733:6022

I start to believe it using metric anyway, while I don't use that 
option. What I missing here?
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