H3C Technologies H3C S7500E Series Switches - Manual (Page 49)

2-7
Label retention mode
There are two label retention modes:
z
Liberal: In this mode, an LSR keeps any received label binding regardless of whether the binding
is from its next hop for the FEC or not. This allows for quicker adaptation to route changes but will
waste label resources as LSRs need to keep extra labels.
z
Conservative: In this mode, an LSR keeps only label bindings that are from its next hops for the
FECs. This allows LSRs to maintain fewer labels but makes LSRs slower in adapting to route
changes.
Currently, the S7500E series supports only the liberal mode.
MPLS Forwarding
LFIB
The LFIB consists of three parts:
z
Next Hop Label Forwarding Entry (NHLFE): Describes the label operation to be performed. It is
used when forwarding MPLS packets.
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FEC to NHLFE (FTN) map: FTN maps each FEC to a set of NHLFEs at the ingress LSR. The
FTN map is used for forwarding unlabeled packets that need MPLS forwarding. When an LSR
receives an unlabeled packet, it looks for the corresponding FIB entry. If the Token value of the
FIB entry is not Invalid, the packet needs to be forwarded through MPLS. The LSR will then look
for the corresponding NHLFE entry according to Token value to determine the label operation to
be performed.
z
Incoming Label Map (ILM): ILM maps each incoming label to a set of NHLFEs. It is used when
forwarding labeled packets. When an LSR receives a labeled packet, it looks for the
corresponding ILM entry. If the Token value of the ILM entry is not null, the LSR will look for the
corresponding NHLFE entry to determine the label operation to be performed.
FTN and ILM are associated with NHLFE through Token.