refer to the 10 point algorithm BGP uses to select a path
How BGP Selects a Path
Path selection is based on the following:
1-If NextHop is inaccessible do not consider it.
2-Prefer the largest Weight.
3-If same weight prefer largest Local Preference.
4-If same Local Preference prefer the route that the specified router has
originated.
5-If no route was originated prefer the shorter AS path.
6-If all paths are external prefer the lowest origin code
(IGP<EGP<INCOMPLETE).
7-If origin codes are the same prefer the path with the lowest MED.
8-If path is the same length prefer the External path over Internal.
9-If IGP synchronization is disabled and only internal path remain prefer
the path through the closest IGP neighbor.
10-Prefer the route with the lowest ip address value for BGP router ID.
Are your iBGP neighbors connected via ethernet with connected routes, some
IGP like RIP or OSPF, or with static routes? Is IGP syncronization enabled?
The answers to these questions play into item # 8. In any case, Local
Preference is considered first.
Thanks, Paul
-----Original Message-----
From: Vinod Anthony Joseph Cherunni [mailto:vac@dsqworld.com]
Sent: Tuesday, December 05, 2000 3:11 AM
To: Suntrup, Paul C, NDINS
Cc: cisco-nsp@puck.nether.net
Subject: RE: [nsp] REG: BGP Attributes
Dear Paul,
Thanks a lot for the advice, One thing is still unclear in regard to the
Local preference.
Assuming I have two circuits to the NAP, One ciruit originating from my
border router in Virginia, & the other from another border router in
california, Also stating that both the border routers of mine are connected
using IBGP internally. Now if I set a local preference for a particular
prefix to say 200 on both my border routers, Will some sort of load
balancing happen, or else will traffic originating from Virginia exit using
the Virginia border router, & vice versa wherein the internal IGP costs are
calculated while traffic exits.
Can I set local preferences between IBGP Peers? Defining it at transit
routers that are not directly connected to external peers.
Kindly advice
With warm regards,
Vinod.
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