BGP path selection Example1: as-path and multipath / load balancer

Owned by Jean-luc KRIKER
Last updated: Nov 08, 2023
2 min read

using virtual tunnel between virtual-router

Example:   BGP Path Selection:


Dual Homed - Dual Router

Ingress traffic / attract traffic on one interface for a Prefix

1- set prefix length on one interface:   /24  and  2 x /25  ( preferred ) 

2-  (pre-pend)+ AS-PATH length for this prefix

3- MED ( for eBGP to #AS )   for this prefix  - - If copied by intermediate AS - - 

( 4- Community or ext-community )


Egress traffic:  to "force traffic on 1 interface "

1- inside set "Local Preference"



Ingress traffic:

Must use transitive Attributes

1- set prefix length on one interface:   /24  and  2 x /25  ( preferred ) 

2-  (pre-pend)+ AS-PATH length for this prefix

3- MED ( for eBGP to #AS )   for this prefix - - If copied by intermediate AS - - 

( 4- Community or ext-community )


Egress traffic:

1- inside set "Local Preference" on one interface


Dual homed - Single router

  • Ingress traffic / attract traffic on one interface for a Prefix:





  • Egress traffic:  to "force traffic on 1 interface "





iBGP
single CPE router with 2 uplink ( RR )

1- loopback as soorce

2- use "from" option to differenciate the 2 uplink

>> the remove will show 2 different NH ( CPE uplinks )