【71-75】Border Gateway Protocol（BGP） is inter-autonomous system （71） protocol. BGP isbasedonarouting method called path vector routing. Distance vector routing is not a good candidateforinter-autonomous system routing because there are occasions on which the route with thesmallest （72） count is not the preferred route. For example， we may not want a packetthroughan autonomous system that is not secure even though it is shortest route. Also， distance vectorroutingis unstable due to the fact that the routers announce only the number of hop counts to thedestinationwithout defining the path that leads to that （73） . A router that receives a distancevectoradvertisement packet may be fooled if the shortest path is actually calculated through thereceivingrouter itself. Link （74） routing is also not a good candidate for inter-autonomous systemroutingbecause an internet is usually too big for this routing method. To use link state routingforthewhole internet would require each router to have a huge link state database. It wouldalsotakealong time for each router to calculate its routing （75） using the Dijkstra algorism.
