Well I am studying BGP more intensely these days. Does anyone have a simple explanation of the difference between an as-path and an as-set?
AS-PATH = ordered list of AS's that describe= uo the path to a destination
AS-SET = unordered list of AS's that describe the path to a destination
So why use an AS-SET. Well it is used when a router has aggregated a number of routes before advertising them on.
The AS-PATH is used to ensure there are no routing loops in the path ie. the same AS should not be seen more than once. But if a router aggregates a number of routes then the AS-PATH info is lost.
So the router that is aggregating the routes can include the actual AS's for the routes it is aggregating in an AS-SET. It doesn't need to be in order because to detect a routing loop you only need to check for the occurence of an AS more than once not the actual order.