The MPLS pseudowire hash label allows LSR nodes in a network to load balance labeled packets in a more granular manner than by hashing on the standard label stack. Using the hash label also removes the need to have an LSR inspect the payload below the label stack to check for an IPv4 or IPv6 header.
In packets forwarded over an LSP, an MPLS hash label is inserted by the ingress LER at the bottom of the label stack. The label value is the result of the hash of the packet headers (the packet header fields that are used depend on the capability of the ingress LER node). The ingress LER hash routine guarantees that the spraying of packets by an LSR hashing on the extended label stack, which includes the hash label, maintains packet ordering within a conversation. LSR hashing pertains to multiple LDP ECMP paths or multiple paths over a LAG network port.
On 7210 SAS devices, the ingress node does not use the pseudowire hash label for ECMP hashing and LAG hashing. It is available for use by the transit MPLS LSR nodes. See the 7210 SAS-D, Dxp, K 2F1C2T, K 2F6C4T, K 3SFP+ 8C Interface Configuration Guide for a description of the fields used by the ingress LER for ECMP and LAG hashing.
The pseudowire hash label is supported for VLL services with spoke-SDP, VPLS services with spoke-SDP and mesh SDP, and RVPLS services with spoke-SDP.
When a hash label is added at the ingress LER, it is marked with an LSP EXP value of 0.