Internet Group Management Protocol MIB
obsoleted by
- rfc-5519 — Multicast Group Membership Discovery MIB
Extracted elements (27)
igmpCacheExpiryTime explicitly notes that implementations may process local membership reports the same way as reports from other hosts, so a value of 0 (present only due to igmpCacheSelf) is not required — this accommodates differing local-membership handling strategies across implementations.
igmpInterfaceProxyIfIndex is included to model devices that implement IGMP proxying, where memberships on a downstream (host-side) interface trigger Host Membership Reports on an upstream (router-side) interface. Such devices implement the igmpV2RouterMIBGroup only on their router interfaces (those with non-zero proxy index), and the typical default value is 0 (no proxying).
Since IGMP is specific to IPv4, this MIB does not support management of equivalent multicast functionality for other address families such as IPv6. Management of IPv6 multicast may be supported by other MIBs.
The MIB module is compliant to SMIv2 but can be translated to SMIv1 with semantic equivalence, except where Counter64 objects must be omitted since no SMIv1 translation is possible. Some machine-readable SMIv2 information will become textual descriptions in SMIv1, which is not considered a semantic change.
This MIB supports IGMPv1 (RFC 1112) and IGMPv2 (RFC 2236) only; a future MIB version will support IGMPv3 (then a work in progress). The entire MIB is applicable to IPv4 multicast routers; a subset applies to IGMP hosts.
All routers on a LAN must be configured to run the same version of IGMP on that LAN. If queries are received with a version different from igmpInterfaceVersion, it indicates a configuration error tracked by igmpInterfaceWrongVersionQueries.
Implementers are recommended to use SNMPv3 with the User-based Security Model (RFC 2574) and View-based Access Control Model (RFC 2575) to secure access to this MIB. SNMPv1 alone is considered an insecure environment even on a network secured by IPsec.
Four compliance statements are defined: igmpV1HostMIBCompliance and igmpV1RouterMIBCompliance for IGMPv1 implementations, and igmpV2HostMIBCompliance and igmpV2RouterMIBCompliance for IGMPv2 implementations. All four permit igmpInterfaceStatus and igmpCacheStatus to be read-only (write access not required).
igmpCacheLastReporter (IpAddress, read-only) holds the source address of the last membership report received for the group on this interface; value is 0.0.0.0 if no report has been received.
igmpCacheSelf (TruthValue, default true) indicates whether the local system is a member of the multicast group on the interface. igmpCacheExpiryTime is zero when the entry exists only because igmpCacheSelf is true; if the router left the group the entry would age out immediately.
igmpCacheTable is indexed by (igmpCacheAddress, igmpCacheIfIndex) and contains 8 columnar objects: local membership flag, last reporter address, up-time, expiry time, row status, and IGMPv1 host timer. Both hosts and routers implement this table.
igmpCacheVersion1HostTimer (TimeTicks, read-only) is the time remaining before the local router assumes no IGMPv1 members exist on the subnet. Reset upon any IGMPv1 Membership Report; while non-zero, the router ignores IGMPv2 Leave messages for this group.
igmpInterfaceLastMembQueryIntvl (Unsigned32, 0–255 tenths of seconds, default 10) is the Max Response Time inserted into Group-Specific Queries sent in response to Leave Group messages, and the interval between such queries. Tuning this value modifies leave latency; it is irrelevant when igmpInterfaceVersion is 1.
igmpInterfaceProxyIfIndex (InterfaceIndexOrZero, default 0) supports IGMP proxying: a non-zero value indicates that memberships learned on this interface cause IGMP Host Membership Reports to be sent on the identified upstream interface. Proxy devices implement igmpV2RouterMIBGroup only on router (non-zero) interfaces.
igmpInterfaceQuerier (IpAddress, read-only) reports the address of the IGMP Querier on the subnet attached to the interface. igmpInterfaceQuerierUpTime records how long ago the querier last changed; igmpInterfaceQuerierExpiryTime reports remaining time before the Other Querier Present Timer expires (zero if local system is querier).
igmpInterfaceQueryInterval specifies the frequency at which IGMP Host-Query packets are transmitted on the interface, in seconds. Default value is 125 seconds.
igmpInterfaceQueryMaxResponseTime is the maximum query response time advertised in IGMPv2 queries, encoded as an Unsigned32 in the range 0–255 tenths of seconds. Default is 100 (10 seconds).
igmpInterfaceRobustness (Unsigned32, range 1–255, default 2) is the Robustness Variable that allows tuning for expected packet loss. IGMP is robust to (Robustness Variable – 1) packet losses; increasing it accommodates lossier subnets.
igmpInterfaceTable is indexed by igmpInterfaceIfIndex (InterfaceIndex) and contains 15 columnar objects covering query intervals, version, querier address, timers, counters, proxy configuration, robustness, and last-member query interval. Rows are created/destroyed via igmpInterfaceStatus (RowStatus) to enable/disable IGMP on an interface.
igmpInterfaceVersion indicates the IGMP version (1 or 2) running on the interface and is read-create to allow router configuration. Default is 2. IGMP requires all routers on a LAN to run the same version.
igmpInterfaceVersion1QuerierTimer (TimeTicks, read-only) is the time remaining until the host assumes no IGMPv1 routers are present on the interface. While non-zero, the host replies to all queries with IGMPv1 membership reports.
igmpInterfaceWrongVersionQueries (Counter32) counts queries received whose IGMP version does not match igmpInterfaceVersion over the lifetime of the row. A non-zero value indicates a configuration error since all routers on a LAN must run the same IGMP version.
Six OBJECT-GROUPs partition objects by role: igmpBaseMIBGroup (all hosts/routers, IGMPv1+v2), igmpRouterMIBGroup (router-only v1/v2), igmpV2HostMIBGroup (host v2 additions), igmpHostOptMIBGroup (optional host objects), igmpV2RouterMIBGroup (router v2 additions), igmpV2ProxyMIBGroup (proxy devices). The base group requires only igmpCacheSelf, igmpCacheStatus, and igmpInterfaceStatus.
The IGMP-STD-MIB module is assigned OID { mib-2 85 } and contains two conceptual tables: igmpInterfaceTable (one row per IGMP-enabled interface) and igmpCacheTable (one row per multicast group per interface). Both tables are intended for implementation by hosts and routers, though some objects apply only to routers.
This document registers the igmpStdMIB MODULE-IDENTITY at OID { mib-2 85 }, last updated 2000-09-28. The MIB objects are under igmpMIBObjects { igmpStdMIB 1 } and conformance information under igmpMIBConformance { igmpStdMIB 2 }.
igmpCacheSelf and igmpCacheLastReporter can be used to identify machines listening to a given multicast group address, exposing potentially sensitive membership information. Unauthorized read access is described as relatively innocuous but still warrants access control.
Unauthorized write access to the read-write/read-create objects (e.g., igmpInterfaceVersion, igmpInterfaceRobustness, igmpInterfaceStatus) could cause a denial of service by misconfiguring IGMP on the router. SET operations in a non-secure environment without proper protection can negatively affect network operations.