cancel
Showing results for 
Search instead for 
Did you mean: 
cancel

Local Preference - BGP

Aneek
Beginner
Beginner

RIB-in --------------> RIB --------------> RIB-out

Q.1. If you receive a route with local preference propagating into RIB-in then what is the local preference of route from RIB-out?

Q.2. If you don't receive a route with local preference propagating into RIB-in then what is the local preference of route from RIB-out?

Pls, let me know the answers. 

#BGP Attributes 

1 REPLY 1

Giuseppe Larosa
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hello @Aneek ,

local preference is a BGP attribute that a single BGP AS scope.

It can be set by a router in order to influence the best path choices of all its iBGP peers ( routers in same BGP AS).

the local preference is not propagated to eBGP peers

The default value of local preference is 100 and the higher value is the better.

 

So if a router receives an iBGP route with a modified value of local preference it will use locally for choising the best path but it will not propagate the BGP advertisement to another iBGP peer unless it is a BGP route reflector server and the route is received by a client.

Locally generated routes can be sent to both eBGP and iBGP peers but only the last ones will see the local preference value configured on the local node if any

 

So Q1 a route is propagated to RIB-out with local preference value unchanged if the local node is a BGP RRS otherwise in RIB out towards eBGP peers if any the route will be sent without the local preference attribute

Q2 may mean if you receive a route without a local preference value attribute it will see it as 100. All the above considerations apply

If Q2 refers to locally generated routes the local node can change the local preference value and that value will be reported in updates sent to all iBGP peers not to eBGP peers

 

Hope to help

Giuseppe

 

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: