A method and system of controlling access to a destination (17, 23, 24) in a data processing network where the destination is limited to a fixed number of requesters responds to a new request (50) for access from a given requestor (20) by determining whether the fixed number would be exceeded. If the fixed number would not be exceeded (51), the new request is granted by connecting (52) the given requester to the destination. If the fixed number would be exceeded, the liveness of the or each current connection to a respective requester is tested (55). If the liveness test succeeds, the new request is rejected but if the liveness test fails, the new request is granted (52).