The present invention provides a method for permitting fully detailed advertising of reachability information for some addresses in a network while efficiently summarizing reachability information for other addresses. At least one embodiment is implemented as part of a process used by logical nodes for advertising reachability information for members of a group of nodes represented by the logical node. At least one embodiment provides an "exception" instruction that allows detailed reachable address information to be advertised for an address that would otherwise be included in summary address information. At least one embodiment allows detailed reachability information to be advertised for the particular address while still allowing summarization of reachable address information for addresses sharing a common prefix with the "exception" address. At least one embodiment thereby allows detailed information to be advertised where needed while allowing summary address information to be advertised where such detailed information is not needed.