BGP Attributes

AC

The two mandatory BGP (Border Gateway Protocol) attributes are the AS Path and Next Hop.

1. AS Path: It is a sequence of AS numbers through which the BGP update has traversed to reach the destination network. It helps to prevent routing loops and ensures that the best path is selected. When a BGP router receives an update, it checks the AS path attribute to see if it has already passed through that AS number, and if it has, it discards the update. The AS Path attribute is also used to determine the shortest path to the destination network.

2. Next Hop: It is the IP address of the next router that should be used to forward traffic towards the destination network. The Next Hop attribute is used to route traffic to the correct next-hop router, which is typically a directly connected neighbor. If the Next Hop attribute is not present in a BGP update, the update is considered invalid and is discarded.

The other two BGP attributes mentioned in the answer choices are optional:

3. Aggregator: This attribute is used to identify the router that performed aggregation (combining multiple prefixes into a single prefix) on behalf of another AS. This attribute is not required for normal BGP operation but is useful for troubleshooting.

4. Community: This attribute is used to tag BGP routes with additional information that can be used to control routing policies within a single AS or between multiple ASes. It is not mandatory but is commonly used for policy-based routing.

In conclusion, the two mandatory BGP attributes are the AS Path and Next Hop.