Management Information Base for Intermediate System to Intermediate System (IS-IS)
Extracted elements (30)
Separate isisSysLevelMetricStyle and isisSysLevelSPFConsiders objects allow an operator to migrate between narrow and wide metrics by first generating both styles, then shifting SPF to consider wide metrics only, achieving a hitless transition as described in RFC 3787.
The isisCircLevelLSPThrottle controls burst rate for back-to-back LSP transmissions (minimum inter-LSP interval in ms), while isisCircLevelMinLSPRetransInt controls the minimum re-send interval for the same LSP (in seconds). These are intentionally separate to address different flooding behaviors.
The isisNextCircIndex scalar uses the DIFFSERV-MIB IndexIntegerNextFree type to coordinate circuit row creation between management applications. A manager reads the scalar, uses the returned non-zero value as the new isisCircIndex in a SET, and retries if inconsistentValue is returned, preventing index collisions.
The ReplaceOnlyWhileDisabled behavior prevents modification of structural circuit attributes (circuit type, level type) while the circuit admin state is 'on', avoiding inconsistent protocol state mid-operation. Objects following this behavior require disabling the row before reconfiguration.
The ResettingTimer behavior specifies that when a timer object is changed mid-interval, the next expiration occurs at the new interval after the original start time (or immediately, whichever is later), preserving interval semantics without abrupt resets. This applies to isisSysMaxLSPGenInt, isisSysWaitTime, hello timers, and SNP intervals.
isisCircMeshGroupEnabled and isisCircMeshGroup implement mesh group flooding reduction from RFC 2973. Circuits in the same mesh group form a virtual multiaccess network; an LSP received on one member circuit is not flooded to other member circuits in the same group.
Tables indexed by InetAddress fields (isisSummAddrTable, isisRedistributeAddrTable) may produce OID instances with more than 128 sub-identifiers if the address and prefix length fields are long. Such OIDs cannot be accessed using SNMPv1, SNMPv2c, or SNMPv3 due to OBJECT IDENTIFIER length constraints.
The MIB includes isisCirc3WayEnabled and isisCircExtendedCircID to support the three-way handshake for point-to-point adjacencies defined in RFC 3373. The extended circuit ID must be unique across all circuits on the IS when 3-way is enabled.
Configured values for MIB objects marked with 'Configured values MUST survive an agent reboot' — including isisSysLevelType, isisSysID, isisSysMaxPathSplits, isisSysMaxLSPGenInt, isisSysAdminState, and all circuit-level parameters — MUST be persisted across restarts.
For isisSummAddrEntry and isisRedistributeAddrEntry, the bitwise AND of the address value with the mask derived from the prefix length MUST equal the address itself; an inconsistentName error MUST be returned on SET or CREATE if the index pair is inconsistent.
If the Intermediate System can reach any subset of a configured summary address range, the summary address MUST be announced instead at the configured metric (isisSummAddrTable). Routes matching an isisRedistributeAddrTable entry MUST be announced at L1 when isisSysL2toL1Leaking is enabled.
isisSysMaxLSPGenInt (maximum interval between generated LSPs) must be greater than any configured isisSysLevelMinLSPGenInt value, and SHOULD be at least 300 seconds less than isisSysMaxAge. isisSysMaxAge SHOULD be at least 300 seconds greater than isisSysMaxLSPGenInt.
The isisManAreaAddrTable MUST contain at least one active row at all times. An attempt to create more than 3 active rows, or to destroy the last active row while isisSysAdminState is 'on', MUST return inconsistentValue.
The overload bit MUST continue to be set if the implementation runs out of memory, independent of the isisSysLevelSetOverload management variable. Administrative clearing of the overload bit via isisSysLevelSetOverloadUntil is only honored when memory is not exhausted.
IsisLevelState defines four operational states for IS-IS at a given level: off (not active), on (active and not overloaded), waiting (low on essential resources such as memory), and overloaded (originating LSPs with the overload bit set).
IsisMetricStyle distinguishes between narrow (RFC 1195, 6-bit), wide (Traffic Engineering, 24/32-bit), and both metric styles, controlling both the style generated in LSPs (isisSysLevelMetricStyle) and the style considered in SPF computation (isisSysLevelSPFConsiders).
The IS-IS MIB defines ten major object groups under isisObjects: isisSystem (1), isisSysLevel (2), isisCirc (3), isisCircLevelValues (4), isisCounters (5), isisISAdj (6), isisReachAddr (7), isisIPReachAddr (8), isisLSPDataBase (9), and isisNotification (10).
The isisCircLevelTable captures per-circuit per-level parameters: default and wide metrics, IS priority for DIS election, hello multiplier, hello timer (10–600000 ms), DR hello timer (10–120000 ms), LSP throttle, minimum LSP retransmit interval, CSNP interval, and PSNP interval.
The isisCircTable defines per-circuit attributes including interface index, admin state, circuit type (broadcast, ptToPt, staticIn, staticOut, dA), level type, mesh group membership, 3-way handshake enablement, and extended circuit ID.
The isisISAdjTable records adjacencies to neighboring Intermediate Systems, indexed by circuit and adjacency index. Each entry includes 2-way and 3-way adjacency state, neighbor SNPA address, system type, system ID, extended circuit ID, usage level, hold timer, neighbor priority, and last-up timestamp.
The isisPacketCounterTable counts IS-IS PDUs by circuit, level (L1/L2), and direction (sending/receiving) across seven types: IIH, ISH, ESH, LSP, CSNP, PSNP, and unknown. Point-to-point IIH PDUs are counted at the lowest enabled level.
The isisSysLevelTable provides per-level configuration including originating LSP buffer size (512–16000 bytes), minimum LSP generation interval, metric style for generation and SPF, Traffic Engineering enablement, and overload controls with optional timed clearing.
The isisSystemCounterTable tracks system-wide events per level including corrupted in-memory LSPs, authentication type and key failures, LSP database overloads, sequence number skips, own LSP purges, ID field length mismatches, partition changes, SPF runs, and received LSPs with errors.
IANA assigned the OID { mib-2 138 } for the isisMIB MODULE-IDENTITY. The MIB is organized under three sub-trees: isisNotifications (0), isisObjects (1), and isisConformance (2).
Several read-write MIB objects can directly affect IS-IS routing behavior: isisSysAdminState can shut down the protocol instance, isisSysLevelSetOverload can force the overload bit causing traffic rerouting, and isisSysL2toL1Leaking can alter route distribution between levels. Unauthorized write access to these objects constitutes a significant routing security risk.
The MIB exposes authentication failure counters (isisSysStatAuthTypeFails, isisSysStatAuthFails, isisCircAuthTypeFails, isisCircAuthFails) that reveal whether IS-IS authentication is in use and whether it is being circumvented. These read-only counters should be protected from unauthorized read access to avoid disclosing security posture.
The MIB provides read-write access to circuit-level timers and metrics (hello timers, metric values, LSP buffer sizes) that, if tampered with, could degrade IS-IS convergence, trigger excessive SPF computation, or cause adjacency failures. SNMP access control mechanisms should restrict write access to authorized managers only.
IsisLinkStatePDUID is an 8-byte OCTET STRING encoding the LSP identifier: a 6-byte SystemID, a 1-byte PseudoNode ID (0 for non-LAN LSPs), and a 1-byte fragment number starting at 0. Non-zero PseudoNode IDs must be unique to the IS but need not match IfIndex.
IsisOSINSAddress is an OCTET STRING of 0–20 bytes representing an OSI Network Service Address (NSAP, SNPA, or Network Entity Title). IsisLSPBuffSize is restricted to Unsigned32 values 512–16000 bytes.
IsisSystemID is a 6-byte OCTET STRING that uniquely identifies an Intermediate System within a network. It is included in all PDUs originated by the IS; bit ordering is used only for tie-breaking in DIS elections.