Influence Traffic with BGP Attributes

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Based on industry best practices, you can use the BGP attributes AS-path (by prepending additional ASs into the outgoing BGP messages) and MED to influence how traffic enters your network.

BGP (Border Gateway Protocol) is a routing protocol used to exchange routing information between different autonomous systems (AS). When multiple paths are available for a destination, BGP uses attributes to select the best path for the traffic. Two important BGP attributes that can be modified to influence how traffic enters your network are:

1. Local Preference: The Local Preference (LP) attribute is used within the same AS to prefer a particular path for inbound traffic. By setting a higher local preference for a certain route, traffic will prefer that route over others with a lower local preference. This attribute is not advertised to other ASs, and is only used within the local AS.

For example, if you have multiple connections to the same ISP and you want to prefer traffic to enter your network through a certain link, you can set a higher local preference for the route learned through that link. The router will prefer that route for inbound traffic.

2. AS Path: The AS Path attribute is used to prevent loops and determine the shortest path between two ASs. It is also used to influence traffic entering your network by manipulating the path length. By adding or removing AS numbers from the AS path, you can make certain routes appear more attractive or unattractive to inbound traffic.

For example, if you want traffic from a certain region to enter your network through a specific link, you can prepend your AS number multiple times to the AS path of the route learned through that link. This will make that path appear longer and less attractive to inbound traffic, causing traffic to prefer other paths with shorter AS paths.

Other BGP attributes that can be used to influence inbound traffic include Next Hop and MED (Multi-Exit Discriminator). However, these attributes are less commonly used for this purpose, and are typically used for other functions such as load balancing and path selection within an AS.