Lfib, Control plane and forwarding plane – H3C Technologies H3C Intelligent Management Center User Manual
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S—One bit in length. MPLS supports multiple levels of labels. This field is used to indicate whether
a label is at the bottom of the label stack. 1 indicates that the label is at the bottom of the label
stack.
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TTL—Eight bits in length. Like the homonymous IP header field, it is used to prevent loops.
LSR
A label switching router (LSR) is a fundamental component on an MPLS network. LSRs support label
distribution and label swapping.
LER
A label edge router (LER) is an LSR that resides at the edge of an MPLS network and is connected to
another network.
LSP
A label switched path (LSP) is the path along which packets of a FEC travel through an MPLS network. An
LSP is a unidirectional path from the ingress of an MPLS network to the egress. On an LSP, in the packet
transfer direction, two neighboring LSRs are called the “upstream LSR” and “downstream LSR”,
respectively. As shown in
, LSR B is the downstream LSR of LSR A; LSR A is the upstream LSR of
LSR B.
Figure 118 Diagram for an LSP
LFIB
On an MPLS network, labeled packets are forwarded according to the Label Forwarding Information
Base (LFIB), which is like the FIB for IP packet forwarding on an IP network.
Control plane and forwarding plane
An MPLS node consists of two planes, control plane and forwarding plane.
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Control plane—Assigns labels, selects routes, establishes the LFIB, establishes and removes LSPs.
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Forwarding plane—Forwards packets according to the LFIB
As shown in
, the element of an MPLS network is LSR. LSRs in the same routing or administrative
domain form an MPLS domain.
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