Which BGP Attributes Influence Traffic Coming into an AS?

AB

A: The LOCAL_PREF attribute is a well-known attribute that represents the network operator's degree of preference for a route within the entire AS. The larger the value of the local preference, the more preferable the route is.

B: The BGP NEXT_HOP is a well-known mandatory attribute. The Next Hop attribute is set when a BGP speaker advertises a prefix to a BGP speaker outside its local autonomous system (it may also be set when advertising routes within an AS, this will be discussed in later sections). The Next Hop attribute may also serve as a way to direct traffic to another speaker, rather than the speaker advertising the route itself

The two BGP attributes that influence traffic coming into an Autonomous System (AS) are local preference and MED (Multi-Exit Discriminator).

1. Local Preference: Local preference is an optional, non-transitive BGP attribute that is used to indicate to the neighboring Autonomous Systems (AS) which path has a higher preference for incoming traffic. Local preference is set within the AS and is used to influence how traffic is routed within the AS. When a BGP router receives multiple routes for the same destination, it selects the route with the highest local preference as the best path.

For example, if an AS has two connections to another AS, one connection with a local preference of 200 and another with a local preference of 100, traffic entering the AS through the first connection is preferred because it has a higher local preference value.

2. Multi-Exit Discriminator (MED): Multi-Exit Discriminator (MED) is an optional, non-transitive BGP attribute that is used to influence the path selection of incoming traffic from different ASes. The MED is typically used by an AS to indicate to its neighboring ASes which path it prefers for outbound traffic to reach a particular destination.

For example, if an AS has two connections to another AS, it can set a lower MED value for the path it prefers for outbound traffic to a particular destination. In this case, the neighboring AS will prefer to send traffic for that destination to the AS with the lower MED value.

Note that MED only influences inbound traffic into an AS, and it is not guaranteed to work in all scenarios. Additionally, MED is not always honored by all BGP routers.

Next hop and origin are not attributes that influence traffic coming into an AS. The next hop attribute is used to specify the IP address of the next hop router on the path to the destination network, while the origin attribute is used to indicate the origin of the BGP route (i.e., whether the route was learned via an interior or exterior gateway protocol).