At an Internet Exchange point, many ISPs are connected to each other by
external BGP peering. Normally these external BGP connection are done by
full mesh method. As with internal BGP full mesh formation,
this method has a scaling problem.
This scaling problem is well known. Route Server is a method to resolve the problem. Each ISP's BGP router only peers to Route Server. Route Server serves as BGP information exchange to other BGP routers. By applying this method, numbers of BGP connections is reduced from O(n*(n-1)/2) to O(n).
Unlike normal BGP router, Route Server must have several routing tables
for managing different routing policies for each BGP speaker. We call the
routing tables as different views. bgpd can work as
normal BGP router or Route Server or both at the same time.