BGP attribute with ISP

[Leftz]

Hi Company has two links to ISP or two ISPs. There are a few bgp attributes that can be used to decide which link of the two can be primary or second link. such as for route inbound local preference, weight, and outbound MED and as-path etc.

So usually which one or two bgp attributes are often used on company side router for us to easily control routes?

Anyone can share this? Thanks

[MHM Cisco World]

Both needed inbound and outbound to have symmetric traffic.

[Leftz]

too simple. can you tell a little bit more

[MHM Cisco World]

https://cordero.me/bgp-best-path-selection-manipulation/

check this link

[M02@rt37]

Hello @Leftz 

-Local Preference:

Inbound Attribute: Local Preference is used within the autonomous system (AS) to influence the selection of the exit point for outbound traffic. A higher local preference value indicates a preferred route. Set a higher local preference on the router for the preferred link.

-AS-Path Prepending:

Outbound Attribute: AS-Path Prepending involves adding the router's own AS number multiple times to the AS-path of the route being advertised to make it less attractive to incoming traffic. By prepending more AS numbers to one link's routes, you can influence inbound traffic to prefer the other link.

You have also:

-MED:

Outbound Attribute: MED is used to influence the selection of the exit point for incoming traffic in a neighboring AS. You can set a lower MED for the preferred link.

-BGP Community Values:

Inbound/Outbound Attribute: Using BGP community values allows you to tag routes with specific attributes. You can define and apply communities to routes to control their behavior within your AS or influence how they are treated by ISPs.

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

--Note that the effectiveness of these attributes can depend on the specific policies and configurations of your ISPs. It's recommended to coordinate with your ISPs to check these policies.

[Leftz]

I know these mechanism or theroy on how bgp attribute to work for selection. all of your reply did not answer my question. for example, for inbound route, we can use local preference or weight on company side, but ISP side also can use MED or as path to control outbound routes for the same direction. so Usually what attribute company prefer to use so that they can easily control routes on company side router. 

[MHM Cisco World]

do you access to ISP to control the traffic  ? 
NO you access to your Router and you can use LP or weight direction of route-map IN.
that answer which side you can access make you select the way you can control traffic.

MHM