Pseudowire (PW) over MPLS PSN Management Information Base (MIB)
Extracted elements (23)
Inbound tunnel-to-PW mapping is not configured or reported through this MIB because the local PE does not know the inbound association between specific PWs and MPLS tunnels — that information resides at the remote PE.
The MIB assumes a PW can be associated to one MPLS-TE tunnel at a time, which may have multiple LSP instances. Selection of the active LSP is outside the MIB's scope (it is part of MPLS PSN functionality); only the current active LSP is reported.
The PW-MPLS-STD-MIB supports three MPLS network configurations: MPLS-TE (tunnels via MPLS-TE-STD-MIB), non-TE (LDP or manual tunnels via XC index in MPLS-LSR-STD-MIB), and PW-label-only (no outer tunnel, for adjacent PEs). A combination of MPLS-TE and LDP outer tunnels for the same PW is allowed, with pwMplsOutboundTunnelTypeInUse indicating which is active.
For signaled MPLS PSN, even across a single hop, there is an MPLS tunnel entry in the relevant MPLS MIB modules. The pwOnly(2) mode (PW label only, no outer tunnel) applies only for manual configuration of PW over a single hop between adjacent PEs.
When using PHP (Penultimate Hop Popping) for the outer tunnel label, the actual packet may not carry the outer MPLS tunnel label, but tunnel entries still exist in the relevant MPLS MIB modules. The applicable mode remains either MPLS-TE or non-TE, not pwOnly.
For the pwMplsOutboundTeGroup, the compliance statement specifies this group MUST be supported if the implementation allows MPLS-TE tunnels to carry PW traffic. At least one of mplsTe(0) or mplsNonTe(1) MUST be supported if PW signaling is supported.
Manual entries in pwMplsTable SHOULD be preserved after a reboot, and the agent MUST ensure the integrity of those entries. If entries are found to be nonconsistent after reboot, the PW pwOperStatus MUST be declared as down(2).
pwMplsOutboundLsrXcIndex MUST return a value of zero if pwMplsMplsType mplsNonTe(1) bit is not set. Similarly, pwMplsOutboundTunnelIndex, pwMplsOutboundTunnelInstance, pwMplsOutboundTunnelLclLSR, and pwMplsOutboundTunnelPeerLSR MUST return zero if the mplsTe(0) bit is not set.
Since tunnels are unidirectional, a pair of tunnels MUST exist (one for inbound, one for outbound) to support a PW connection over MPLS PSN.
SNMPv3 VACM and USM MUST be used with any v3 agent that implements this MIB module. Deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED; SNMPv3 with cryptographic security is RECOMMENDED instead.
The last two octets of the LDP identifier in pwMplsLocalLdpID MUST always both be zeros, as PW labels are always set from the per-platform label space.
The PW-MPLS-STD-MIB module is organized into three MIB layers: a service-specific layer, the general PW MIB layer (RFC5601), and the PSN-specific layer. This document defines the PSN layer for MPLS, associating PWs to MPLS tunnels.
The pwMplsExpBitsMode object determines how EXP bits on the PW shim label are set: outerTunnel(1) copies from the outer tunnel, specifiedValue(2) uses the value in pwMplsExpBits, and serviceDependant(3) uses an implementation-specific rule. Default is outerTunnel(1).
The pwMplsInboundTable provides the XC index (pwMplsInboundXcIndex) in the MPLS-LSR-STD-MIB for the inbound direction of signaled PWs. It is agent-created for each signaled PW and is read-only.
The pwMplsMplsType object is a BITS field indicating the outer tunnel type: mplsTe(0) for MPLS-TE tunnels, mplsNonTe(1) for LDP or manually configured tunnels, and pwOnly(2) for no outer tunnel. A combination of mplsTe(0) and mplsNonTe(1) MAY exist, but pwOnly(2) cannot be combined with the others.
The pwMplsNonTeMappingTable maps PWs to non-TE outbound tunnels, inbound XC entries, or physical interfaces, indexed by direction (psnBound/fromPsn), XC index, ifIndex, and PW index. It enables quick retrieval of PWs carried over specific non-TE tunnels or interfaces.
The pwMplsOutboundTable augments pwMplsEntry and reports or configures the current outbound MPLS tunnel or physical interface carrying PW traffic. It includes objects for MPLS-TE tunnel indexes, non-TE XC index, physical ifIndex, and the currently active tunnel type via pwMplsOutboundTunnelTypeInUse.
The pwMplsOutboundTunnelTypeInUse object reports the currently active tunnel: notYetKnown(1), mplsTe(2), mplsNonTe(3), or pwOnly(4). It is read-only and indicates which path is actively forwarding PW traffic.
The pwMplsTable contains MPLS-specific parameters for each PW when pwPsnType is mpls(1). It is indexed by pwIndex and is automatically created by the agent. Key fields include pwMplsMplsType (BITS: mplsTe, mplsNonTe, pwOnly), pwMplsExpBitsMode, pwMplsExpBits, pwMplsTtl, pwMplsLocalLdpID, pwMplsLocalLdpEntityIndex, pwMplsPeerLdpID, and pwMplsStorageType.
The pwMplsTeMappingTable maps PWs to MPLS-TE outer tunnel head-ends, indexed by tunnel index, tunnel instance, peer LSR ID, local LSR ID, and PW index. It allows quick retrieval of PWs configured on a specific MPLS-TE tunnel and reports the active LSP instance.
IANA assigned the OID { mib-2 181 } for pwMplsStdMIB, recorded in the SMI Numbers registry.
Read-only objects in the PW MPLS MIB tables (pwMplsTable, pwMplsOutboundTable, pwMplsNonTeMappingTable, pwMplsTeMappingTable) may be sensitive as they reveal PW-over-MPLS association information. Administrators should control GET/NOTIFY access and consider encrypting values sent over the network.
The pwMplsTable, pwMplsNonTeMappingTable, and pwMplsTeMappingTable contain objects to provision PW over MPLS tunnels. Unauthorized SET access could result in traffic disruption; SNMPv3 with VACM and USM should be used. Even read access may be sensitive as it reveals PW-to-tunnel association details.