The BGP MED Attribute

BC

MED is used to help influence the preferred path back into the autonomous system when multiple links exist between the same two autonomous systems. BGP routes do not require the MED attribute. If it is missing, BGP assumes the MED value is 0.

The BGP MED (Multi-Exit Discriminator) attribute is an optional non-transitive attribute that is used to influence the path selection process of BGP. It is used to convey to an adjacent AS the preferred path for outbound traffic, in case there are multiple connections between the same two ASes. Here are the correct statements about the BGP MED attribute:

A. It has a default value of 100: This statement is true. The MED attribute has a default value of 100, which means that if no value is specified for the MED attribute, a value of 100 will be used.

C. It is designed for use when multiple connections exist between the same two autonomous systems: This statement is also true. The MED attribute is used to influence the path selection process when multiple connections exist between the same two ASes. The AS that receives the MED attribute will use it to determine the best path for outbound traffic.

B. It has an assumed value of 0: This statement is not true. The MED attribute does not have an assumed value of 0. If no MED attribute is received, it is assumed to have a value of 100.

D. It is designed for use when a BGP router is peering with at least two different autonomous systems: This statement is not true. While it is true that the MED attribute can be used in multi-homed environments where a BGP router is peering with multiple ASes, it is not a requirement. The MED attribute can be used even if a router is peering with only one AS.

In summary, the correct statements about the BGP MED attribute are that it has a default value of 100, and it is designed for use when multiple connections exist between the same two autonomous systems.