Best practices for influencing outbound network traffic

B

The BGP local-preference attribute can be used to influence how traffic leaves your network. BGP uses the local-preference attribute only within an AS. Local preference values are not transmitted across EBGP links.

Of the four BGP attributes mentioned in the question, the one that would typically be modified to influence how traffic leaves a network is the local preference attribute (option B).

BGP, or Border Gateway Protocol, is used by internet service providers and other large networks to exchange routing information and determine the best path for traffic to take between different networks. BGP attributes are used to provide information about the characteristics of different routes, and to help determine the best path for traffic.

The local preference attribute is one of several BGP attributes that can be used to influence routing decisions. It is a value that is assigned to a route by the local router, and is used to indicate the degree of preference that the local router has for that route. Higher values of local preference are preferred over lower values.

By adjusting the local preference attribute for different routes, a network operator can influence how traffic is routed through their network. For example, if a network operator wants to prioritize traffic leaving their network through a particular router or link, they could set a higher local preference for the routes that use that router or link. This would make those routes more attractive to other routers on the network, and increase the likelihood that traffic would be routed through that link.

The other BGP attributes mentioned in the question can also be used to influence routing decisions in different ways:

• MED (Multi-Exit Discriminator) is an optional attribute that is used to indicate the preferred exit point from a network for traffic that is destined for a particular prefix. It is typically used in multi-homed networks to help other networks determine the best path for traffic to take to reach a particular destination. However, modifying the MED attribute on a route does not typically influence how traffic leaves a network, but rather how traffic enters the network from other providers.

• AS-path is another BGP attribute that is used to provide information about the path that a route has taken through different AS (Autonomous System) networks. This attribute is typically used to prevent routing loops and to provide some indication of the stability of different routes. However, modifying the AS-path attribute on a route does not typically influence how traffic leaves a network, but rather how traffic enters the network from other providers.

• Communities are another optional BGP attribute that can be used to group routes together based on certain characteristics, such as geographic location or customer type. They are typically used to simplify the management of large BGP networks and to allow for more granular control over routing decisions. However, modifying the community attribute on a route does not typically influence how traffic leaves a network, but rather how traffic is routed within a network.