IP Version 6 Management Information Base for The Multicast Listener Discovery Protocol
obsoleted by
- rfc-5519 — Multicast Group Membership Discovery MIB
Extracted elements (28)
Both the Interface Table and Cache Table are designed to be implemented by both hosts and routers. Router-only objects are separated into mldRouterMIBGroup so that simpler host implementations need not carry router-specific state.
mldInterfaceVersion is explicitly described as a placeholder to allow future MLD versions to be introduced without changing the table structure, anticipating protocol evolution beyond RFC 2710's version 1.
The MIB is specified as SMIv2-compliant with the note that an SMIv1-compliant version can be produced by translation, except that Counter64 objects cannot be translated and some machine-readable information will become textual descriptions — a loss not considered to change MIB semantics.
The MIB module is based on the IGMP MIB (authored by McCloghrie, Farinacci, and Thaler) adapted for IPv6 and MLD, maintaining structural consistency with the IPv4 multicast management approach.
Proxy devices implementing mldInterfaceProxyIfIndex should implement mldRouterMIBGroup only on router interfaces (those with non-zero mldInterfaceProxyIfIndex), not on the listener-facing interfaces where memberships are learned.
Some implementations may process Membership Reports from the local system the same way as reports from other hosts, meaning mldCacheExpiryTime is not required to be 0 when mldCacheSelf is true and no external reporters exist.
Hosts implementing the MLD MIB MUST support mldBaseMIBGroup (mldCacheSelf, mldCacheStatus, mldInterfaceStatus) and mldHostMIBGroup (mldInterfaceQuerier). Write access to mldInterfaceStatus is not required for host compliance.
Routers implementing the MLD MIB MUST support mldBaseMIBGroup and mldRouterMIBGroup (which adds query interval, join counters, querier state, version, max response delay, robustness, and last-listen-query-interval objects). Write access to mldInterfaceStatus is not required.
The document RECOMMENDS that implementers use SNMPv3 with the User-based Security Model (RFC 2574) and View-based Access Control Model (RFC 2575) to protect MIB access, rather than the insecure SNMPv1 environment.
mldCacheAddress (InetAddressIPv6, SIZE 16) and mldCacheIfIndex (InterfaceIndex) jointly index the Cache Table, uniquely identifying a multicast group–interface pairing.
mldCacheExpiryTime (TimeTicks, read-only) gives the minimum remaining time before a cache entry is aged out. A value of 0 indicates the entry persists only due to local membership (mldCacheSelf true) and would be removed immediately if the router left the group.
mldCacheLastReporter (InetAddressIPv6, SIZE 16, read-only) records the source IPv6 address of the most recently received membership report for a group on this interface. If no report has been received the value is 0::0.
mldCacheSelf (TruthValue, default true) indicates whether the local system is itself a member of the multicast group on this interface. A cache entry with mldCacheSelf true and mldCacheExpiryTime 0 exists solely because of local membership.
mldInterfaceJoins (Counter32, read-only) counts the total number of times a group membership has been added on an interface, providing a long-term indicator of MLD activity volume.
mldInterfaceLastListenQueryIntvl (Unsigned32, default 1 second) is the Last Member Query Interval — both the Max Response Delay in Group-Specific Queries and the spacing between such queries. Reducing it lowers leave latency at the cost of more query traffic.
mldInterfaceProxyIfIndex (InterfaceIndexOrZero, default 0) identifies the upstream interface to which MLD Multicast Listener Reports are forwarded when MLD proxying is active. A value of 0 indicates no proxying.
mldInterfaceQuerier (InetAddressIPv6, SIZE 16) is a read-only object containing the IPv6 address of the MLD Querier on the subnet attached to the interface. It is accompanied by mldInterfaceQuerierUpTime and mldInterfaceQuerierExpiryTime for querier state tracking.
mldInterfaceQueryInterval (Unsigned32, default 125 seconds) specifies the frequency at which MLD Host-Query packets are transmitted on an interface. It is read-create, allowing management configuration.
mldInterfaceQueryMaxResponseDelay (Unsigned32, default 10 seconds) specifies the maximum query response time advertised in MLD queries. It is read-create and affects how quickly group membership changes are detected.
mldInterfaceRobustness (Unsigned32, default 2) is the MLD Robustness Variable, which tunes packet-loss tolerance. MLD is robust to (Robustness Variable - 1) packet losses; increasing the value on lossy subnets is recommended per RFC 2710 Section 7.1.
mldInterfaceStatus and mldCacheStatus (both RowStatus, read-create) control lifecycle of interface and cache entries respectively. Activating an mldInterfaceStatus row enables MLD on the interface; destroying it disables MLD.
mldInterfaceVersion (Unsigned32, default 1) records which version of MLD is running on the interface. The object is described as a placeholder to accommodate future MLD versions beyond RFC 2710.
The MLD Cache Table (mldCacheTable) contains one conceptual row per IPv6 multicast group that has members on a particular interface, indexed by mldCacheAddress and mldCacheIfIndex. It tracks membership state including last reporter and expiry time.
The MLD Interface Table (mldInterfaceTable) contains one conceptual row per interface on which MLD is enabled, indexed by mldInterfaceIfIndex. It holds query parameters, querier state, and counters applicable to both hosts and routers.
The mldMIB module is assigned OID { mib-2 91 }, registering the MLD MIB under the standard SNMP mib-2 subtree. This is the primary IANA registration created by this document.
mldCacheSelf and mldCacheLastReporter can be used to identify which machines are listening to a given multicast group address, creating a privacy-relevant information disclosure risk for readable MIB objects.
SNMPv1 is inherently insecure: even on an IPsec-protected network it provides no per-principal access control for SET operations. The document explicitly flags this and recommends SNMPv3 as the mitigation.
Unauthorized SET operations on the write-able MIB objects (e.g., query interval, robustness, cache status) could cause a denial of service by disrupting MLD operation. Support of SET operations in a non-secure environment without proper protection has a negative effect on network operations.