This architecture change extended the addressing capacity of the Internet but did not prevent IP address exhaustion. The problem was that many sites needed larger address blocks than a Class C network provided, and therefore they received a Class B block, which was in most cases much larger than required. Due to the rapid growth of the Internet, the pool of unassigned Class B addresses (214, or about 16,000) was rapidly being depleted. Classful networking was replaced by Classless Inter-Domain Routing (CIDR), starting in 1993 with the specification of RFC 1518 and RFC 1519, to attempt to solve this problem.