An Analysis of Anycast Architecture and Transport Layer Problems

The Internet Protocol anycasting communication service has been designed to support service locating to the nearest anycast server based on routing protocol measure of distance for anycast service from a pool of identical service servers. The birth of IPv6 has given opportunity to design and implement anycast service at IP layer, which could not be implemented in IPv4 due to addressing complexity. In this paper we analyze and compare the anycast architecture for IPv4 and IPv6. Pitfalls in the new proposed IPv6 anycast design has been identified and solutions to the problems have been proposed. The nature of anycast service, which delivers anycast datagrams to the nearest anycast server independent of previous datagrams, will cause unexpected results if the packets have been fragmented. The fragmented packets may be delivered to different anycast servers and will not be useful for the anycast clients. To obviate the problem we have proposed new protocols at transport layer for anycast messaging between anycast clients and servers for service locating and obtaining information from the servers. FTP client and server applications have been modified to demonstrate the applicability of the proposal.