Penultimate Hop Popping; Label Binding; Label Space Partitioning - Extreme Networks BlackDiamond 6800 MPLS Installation And User Manual

Configuring the MPLS Module

Penultimate Hop Popping

Penultimate hop popping (PHP) is an LSR label stack processing optimization feature.
When enabled, the LSR can "pop" (or discard) the remaining label stack and forward
the packet to the last router along the LSP as a normal Ethernet packet.
By popping the label stack one hop prior to the LSP egress router, the egress router is
spared having to do two lookups. After the label stack has been popped by the
penultimate hop LSR, the LSP egress router must only perform an address lookup to
forward the packet to the destination.
PHP label advertisements using implicit NULL labels can be optionally enabled.
Support for receiving implicit NULL label advertisements by neighbor LSRs is always
enabled. For example, if an LSR advertises implicit NULL labels for IP prefixes, the
neighbor LSRs must support PHP.

Label Binding

Label binding is the process of, and the rules used to, associate labels with FECs. LSRs
construct label mappings and forwarding tables that comprise two types of labels: labels
that are locally assigned and labels that are remotely assigned.
Locally assigned labels are labels that are chosen and assigned locally by the LSR. For
example, when the LSR assigns a label for an advertised direct interface. This binding
information is communicated to neighboring LSRs. Neighbor LSRs view this binding
information as remotely assigned.
Remotely assigned labels are labels that are assigned based on binding information
received from another LSR.

Label Space Partitioning

The Extreme MPLS implementation supports approximately 64 K locally-assigned
labels. The label space is partitioned as described in Table 3-3.
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