Definitions of Managed Objects for the Multiprotocol Label Switching (MPLS), Label Distribution Protocol (LDP)
Extracted elements (26)
DEFVAL clauses in the LDP Entity Table are not specified in the LDP Specification (RFC 3036) but are widely used by existing LDP MIB implementations and have been adopted in this module. They may be overridden at row creation or via subsequent SET requests.
The mplsLdpEntityGenericLRTable in MPLS-LDP-GENERIC-STD-MIB does not exist in the LDP Specification; it was added at the MPLS Working Group's request as a useful mechanism for reserving a range of generic (per-platform) labels.
The mplsLdpPeerTable is separate from the mplsLdpSessionTable to model the distinction between values a peer proposes during discovery/initialization (peer table) and the values actually negotiated for the session (session table), since they may differ.
Two separate notifications (mplsLdpSessionUp and mplsLdpSessionDown) were defined rather than a single combined notification because some NMS applications can more easily match a SessionDown event to a prior SessionUp than parse a varbind list in a unified SessionChange notification.
The MPLS-LDP-STD-MIB imports IndexInteger and IndexIntegerNextFree from DIFFSERV-MIB (RFC 3289), and InetAddressPrefixLength, InetAddressType, InetAddress, and InetPortNumber from INET-ADDRESS-MIB (RFC 3291), making it dependent on these external MIB modules.
The MplsAtmVcIdentifier TEXTUAL-CONVENTION (defined in MPLS-TC-STD-MIB, RFC 3811) restricts VCI values to be greater than 31, implementing the constraint from RFC 3035 for ATM label switching. This differs from the base LDP Specification.
When there is a Path Vector Limit mismatch between an LDP Entity and its Peer during session initialization, the session uses the Entity's configured Path Vector Limit value. A mplsLdpPathVectorLimitMismatch notification is sent to alert the operator of the discrepancy.
If an mplsLdpEntityIndexNext value of zero is retrieved, that indicates no rows can be created in mplsLdpEntityTable at that time; the operator must use this retrieved value when creating new entity rows.
If MIB objects used in LDP Session Initialization need to be modified after session start, the entire session must be halted: the operator sets mplsLdpEntityAdminStatus to disable(2), all session information is discarded, objects are modified, and then admin status is re-enabled to initiate a new session.
The MPLS-LDP-STD-MIB Module MUST be implemented and at least one of the Layer 2 MIB Modules MUST be implemented on an LSR or LER. Ethernet requires MPLS-LDP-GENERIC-STD-MIB; ATM requires MPLS-LDP-ATM-STD-MIB; Frame Relay requires MPLS-LDP-FRAME-RELAY-STD-MIB; all three media require all four modules.
The mplsLdpLsrId scalar object MUST be a globally unique value, such as the 32-bit router ID assigned to the LSR.
The receiving LSR MUST calculate the maximum PDU length for the session by using the smaller of its and its peer's proposals for Max PDU Length. A proposed value of 255 or less specifies the default maximum length of 4096 octets.
Four LDP-specific SNMP notifications are defined: mplsLdpInitSessionThresholdExceeded (session initialization retry count exceeds mplsLdpEntityInitSessionThreshold; a value of 0 disables), mplsLdpPathVectorLimitMismatch (PVL mismatch between entity and peer), mplsLdpSessionUp, and mplsLdpSessionDown.
mplsLdpEntityHelloHoldTimer uses 0 as a sentinel for default values: if 0 and mplsLdpEntityTargetPeer is false, the effective default is 15 seconds (link hello); if 0 and mplsLdpEntityTargetPeer is true, the effective default is 45 seconds (targeted hello). A value of 65535 means infinite.
The mplsLdpEntityStatsTable augments mplsLdpEntityTable with read-only Counter32 objects tracking: session attempts (NAK'd initializations), session rejections by cause (no hello, advertisement mode, max PDU, label range), fatal protocol errors (bad LDP identifier, PDU/message/TLV length, malformed TLV), keepalive timer expiry, and shutdown notifications sent and received.
The mplsLdpEntityTable is indexed by mplsLdpEntityLdpId and mplsLdpEntityIndex, and contains read-create configuration objects: protocol version (DEFVAL 1), admin/oper status, TCP port (DEFVAL 646), UDP discovery port (DEFVAL 646), max PDU length (DEFVAL 4096), keepalive hold timer (DEFVAL 40s), hello hold timer, session threshold, label distribution method, label retention mode, path vector limit, hop count limit, transport address kind (DEFVAL loopback), targeted peer flag, and label type.
The mplsLdpFecTable stores FEC (Forwarding Equivalence Class) element information configurable by the operator, and the mplsLdpLspFecTable associates FECs with LSPs. These are the only tables in MPLS-LDP-STD-MIB not exclusively populated by the LDP protocol.
The mplsLdpHelloAdjacencyTable tracks all adjacencies between LDP entities and peers, indexed by entity LDP ID, entity index, peer LDP ID, and adjacency index. Each entry records hold time remaining (65535 = infinite), negotiated hold time, and adjacency type (link or targeted). A session with zero Hello Adjacencies should be removed.
The mplsLdpPeerTable is a read-only table populated by the LDP protocol, indexed by entity LDP ID, entity index, and peer LDP ID. It contains the peer's LDP identifier, label distribution method, path vector limit, and transport address type and value learned during session initialization.
The mplsLdpSessionPeerAddrTable is a read-only extension of mplsLdpSessionTable that stores peer addresses learned via Address Message advertisement after session initialization, allowing management systems to track all addresses advertised by a peer.
The mplsLdpSessionTable augments mplsLdpPeerTable and contains negotiated, read-only session parameters: state, role (active/passive/unknown), negotiated protocol version, keepalive hold time remaining, negotiated keepalive time (minimum of both proposals), negotiated max PDU length, and a discontinuity timestamp that changes when a session is replaced by a new one.
The optional mplsInSegmentLdpLspTable and mplsOutSegmentLdpLspTable map LDP LSPs to the MPLS-LSR-STD-MIB's mplsInSegmentTable and mplsOutSegmentTable respectively. They are indexed by the LDP session triple plus the LSR MIB segment index, and are only required if the LSR MIB segment tables are implemented.
IANA assigned OIDs under mplsStdMIB for all four MIB modules defined in this document: MPLS-LDP-STD-MIB (mplsStdMIB 4), MPLS-LDP-ATM-STD-MIB, MPLS-LDP-FRAME-RELAY-STD-MIB, and MPLS-LDP-GENERIC-STD-MIB.
Deployment of SNMP versions prior to SNMPv3 is not recommended for managing LDP MIB objects. SNMPv1 and SNMPv2c are community-string-based and not considered secure, exposing LDP configuration to unauthorized read or modification.
Several MPLS-LDP-STD-MIB objects have MAX-ACCESS read-create and can be used to reconfigure or destroy LDP sessions, potentially disrupting MPLS forwarding for all traffic using affected LSPs. SNMPv3 with authentication (authNoPriv or authPriv) is strongly recommended to prevent unauthorized modification.
mplsLdpSessionState models the RFC 3036 Section 2.5.4 Initialization State Machine with five states: nonexistent(1), initialized(2), openrec(3), opensent(4), and operational(5). Session rows appear in the table during initialization (state 2) and are removed when the session is torn down.