Multicast scoping is a technique that can be used to limit multicast traffic by configuring it to an administratively defined topological region. Major objectives of scoping are to relieve stress on scarce resources, such as bandwidth, and to improve privacy or scaling properties. IP multicast implementations can achieve some level of scoping by using the time-to-live (TTL) field in the IP header. However, TTL scoping has proven difficult to implement reliably, and the resulting schemes often are complex and difficult to understand. Administratively scoped IP multicast provides clearer and simpler semantics for multicast scoping. The key properties of administratively scoped IP multicast are that packets addressed to administratively scoped multicast addresses do not cross configured admin-istrative boundaries, and administratively scoped multicast addresses are locally assigned, and hence are not required to be unique across administrative boundaries. The administratively scoped IPv4 multicast address space is the range 239.0.0.0 through 239.255.255.255 . The structure of the IPv4 administratively scoped multicast space is based loosely on the IPv6 addressing architecture as described in RFC 1884. There are two well-known scopes:
The ranges 239.0.0.0/10 , 239.64.0.0/10 , and 239.128.0.0/10 are unassigned and available for expansion of this space. Two other scope classes already exist in IPv4 multicast space: the statically assigned link-local scope, which is 224.0.0.0/24 , and the static global scope allocations , which contain various addresses. Table 9.13 lists the multicast scoping standard supported by the JUNOS software. Table 9.13. Multicast Scoping Standard Supported by JUNOS Software
Configuring Multicast ScopingTo configure multicast scoping, include the following statements: [edit] routing-options { multicast { scope scope-name { interface interface-name ; prefix prefix-range ; } } } |