Multicast Connection Admission Control (MCAC) allows a router to limit bandwidth used by multicast channels, either on a router, on access links, or by an ESM subscriber, by controlling the number of channels that are accepted. When a pre-configured limit is reached, the router prevents receivers from joining any new channels not currently established. By rejecting new channel establishment during an overload condition, the degradation of the quality of the existing multicast service offering is avoided. However, as result, running the MCAC function may cause some channels to be temporarily unavailable to receivers under overload.
Operators can configure one or more MCAC bundle policies (config>router>mcac>policy) to specify multicast channel admission rules and then reference a required MCAC bundle policy on multicast-enabled IPv4 and IPv6 interfaces or group-interfaces. In addition, operators can configure per-interface MCAC behavior.
MCAC is supported on ESM subscriber interfaces as well as multicast interfaces in base router instance, VPLS, and in MVPNs. MCAC is supported for IGMP, IGMP-snooping, MLD, and PIM.
The amount of bandwidth multicast channels can consume is limited by operator-configured unconstrained and mandatory bandwidth values. Those values can be configured on a per-MCAC bundle policy, per subscriber, per interface, and per MCAC interface policy. The bandwidth limits configured for a subscriber or interface limit multicast bandwidth for that particular subscriber or that interface only. The bandwidth limits configured for an MCAC interface policy limit multicast bandwidth across a set of interfaces that share the same interface policy. If bandwidth limits are defined on multiple levels, all level limits must be satisfied for a channel to be admitted. See MCAC algorithm for more information.
MCAC is not applicable to PIM snooping and MLD snooping.