Cisco Systems This document describes a method of providing scope-limited Source- Specific Multicast (SSM) channels by filtering at boundary routers. The filtering prevents SSM traffic from being forwarded through a scope boundary. Each administrative domain that wishes to enforce scoping can choose the sub-range of SSM channels that it wishes to scope -- no globally-scoped address range is defined. The method described here does not require extending the current SSM range allocation to include a new 'scoped SSM' range. The method described is primarily intended to provide scoping for IPv4 SSM channels, since IPv6 integrates multicast scoping into the basic addressing architecture.