IP Multicast MIB
obsoletes
- rfc-2932 — IPv4 Multicast Routing MIB
Extracted elements (26)
Multicast routing protocols are now tracked per-route (ipMcastRouteProtocol) rather than per-interface, because multiple multicast routing protocols may operate on a single interface simultaneously. This is a deliberate departure from the RFC 2932 model.
RFC 5132 obsoletes RFC 2932 (IPMROUTE-STD-MIB) because the earlier MIB supported only IPv4, assumed at most one multicast routing protocol per interface, and was restricted to multicast routing. The new MIB adds IPv6/scoped-address support, allows multiple protocols per interface (now per-route via ipMcastRouteProtocol), and covers non-routing multicast function.
The ipMcastBoundaryIfIndex for IPv6 refers to a virtual intra-node interface rather than an external interface because IPv6 zone boundaries cut through nodes, not links, unlike IPv4 where boundaries cut through links.
ipMcastRouteInIfIndex of 0 indicates that datagrams are not subject to an incoming interface check and may be accepted on multiple interfaces, as in BIDIR-PIM. Similarly, ipMcastRouteUpstreamNeighborType of unknown(0) indicates the upstream neighbor is unknown, as in BIDIR-PIM.
For ipMcastRouteSourceAddressType, if the value is not unknown(0), it MUST be the same as the value of ipMcastRouteGroupType, ensuring address family consistency between source and group addresses in a routing entry.
For IPv6 SSM address ranges in ipMcastSsmRangeTable, only ranges prefixed by FF3x::/16 are permitted, where 'x' is a valid IPv6 RFC 4291 multicast address scope. The syntax of the address range is given by RFC 3306 Sections 4 and 7.
Implementations MUST support SNMPv3 for management access to this MIB. SNMP versions prior to SNMPv3 are not recommended due to lack of adequate security (authentication and privacy), as specified in the compliance statements.
ipMcastBoundaryAddress constrains IPv4 scoped ranges to the 239.0.0.0/8 prefix and IPv6 scoped ranges to FF0x::/16. A boundary for FF0x::/16 implies identical boundaries for FF1x::/16 and FF3x::/16; no separate entries for those prefixes exist in this table.
ipMcastBoundaryTable lists the configured multicast scope zone boundaries per interface. For IPv4, boundaries cut through links (external interfaces). For IPv6, boundaries cut through nodes (virtual internal interfaces, not external).
ipMcastEnabled is a read-write TruthValue scalar that controls whether IP multicast function is enabled on the system. Its storage type is determined by ipMcastDeviceConfigStorageType.
ipMcastInterfaceTable manages per-interface multicast protocol state, indexed by IP version (InetVersion) and interface index. Key columns include ipMcastInterfaceTtl (TTL threshold, 0..256) and ipMcastInterfaceRateLimit (kilobits per second, 0 means no limit).
ipMcastInterfaceTtl defines a TTL/Hop Limit threshold (0..256) for an interface; datagrams with TTL less than this value are not forwarded out the interface. A value of 0 forwards all multicast packets; a value of 256 forwards none.
ipMcastLocalListenerTable identifies local applications or services that have joined multicast groups as listeners, using ipMcastLocalListenerRunIndex to reference the sysApplRunIndex. A value of zero means one or more unidentified applications have joined.
ipMcastRouteDifferentInIfOctets and ipMcastRouteDifferentInIfPackets count packets dropped due to incoming interface checks (RPF check failure in PIM-SM, DF check failure in BIDIR-PIM, etc.). If the rate of increase exceeds 1% of ipMcastRouteOctets, it indicates multicast routing problems requiring investigation.
ipMcastRouteNextHopClosestMemberHops (0..256) gives the minimum hop count to any group member reachable via a given next-hop. Datagrams with TTL/Hop Count less than this value are not forwarded. A value of 0 forwards all; 256 forwards none.
ipMcastRouteNextHopTable contains per-next-hop forwarding information, indexed by group, source, outgoing interface, and next-hop address. The ipMcastRouteNextHopState field uses an INTEGER with values pruned(1) and forwarding(2).
ipMcastRouteSourceAddressType uses a value of unknown(0) to indicate a non-source-specific entry corresponding to all sources in a group. Otherwise, the value MUST be the same as the value of ipMcastRouteGroupType.
ipMcastRouteTable contains multicast routing information for IP datagrams from particular sources to particular IP multicast groups. It is indexed by group address type, group address, group prefix length, source address type, source address, and source prefix length.
ipMcastScopeNameTable provides human-readable, language-tagged names for multicast address scopes, indexed by address type, address prefix, and LangTag. The ipMcastScopeNameDefault flag indicates a preferred language when no desired language name is available.
ipMcastSsmRangeTable holds the configured ranges of multicast group addresses to which Source-Specific Multicast semantics (RFC 3569) should be applied. Entries are indexed by address type, address, and prefix length, and are managed via RowStatus.
ipMcastZoneTable maps each multicast scope zone (identified by InetZoneIndex) to its address range and identifies the default zone index for each scope. Zone index zero is a special value used to request the default zone and is not valid as a table index.
The IPMCAST-MIB module (OID mib-2 168) defines objects for managing IP multicast function including routing, data forwarding, and data reception, independent of the specific multicast protocol in use. It contains two scalars and eight tables.
RFC 5132 requests IANA to assign OID mib-2 168 for the IPMCAST-MIB MODULE-IDENTITY. The document also references IANA-RTPROTO-MIB for IANAipRouteProtocol and IANAipMRouteProtocol values used in routing tables.
Read-only objects such as routing table entries, forwarding statistics, and local listener information could reveal sensitive network topology details to an attacker. SNMPv3 with authentication and privacy should be used to protect read access as well.
Write-capable objects in the MIB (such as ipMcastEnabled, interface TTL thresholds, rate limits, SSM range entries, scope boundaries, and scope names) can disrupt multicast service if manipulated by unauthorized parties. SNMPv3 with authentication and privacy (authPriv) is required to protect against unauthorized access.
ipMcastRouteNextHopState models a two-state machine for each multicast next-hop: pruned(1) indicates the outgoing interface is not currently forwarding, and forwarding(2) indicates it is. The ipMcastRouteNextHopExpiryTime represents time until a prune expires and state reverts to forwarding(2).