Path Vector Algorithms, such as BGP, are similar to a distance vector protocol. The major difference between the two is that instead of looking at just distance to determine a loop free path to the destination, various other attributes are considered instead, in the case of BGP:
- Autonomous system path (AS_Path)
- Multi exit discriminator (MED)
- Next hop
- Local preference
- Atomic aggregate
Path vector protocols such as BGP guarantee a loop free path by keeping records of each autonomous system (AS) that the route advertisement traverses. If the router receives an advertisement where it is already part of the AS_Path, it is rejected.