Mpls Architecture - 3Com 8807 Configuration Manual

510 C 47: MPLS A
HAPTER

MPLS Architecture

MPLS Network Structure
RCHITECTURE
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Currently, the Switch 8800 Family series adopt the ordered label control mode.
5 Label retention mode
There are two label-retention modes: liberal label retention mode and conservative
label retention mode.
Suppose there are two LSRs: Ru and Rd. For a specific FEC, if LSR Ru has received
the label binding from LSR Rd, in case Rd is not the next hop of Ru and Ru saves
this binding, then it is the liberal label retention. And if Ru discards this binding,
then it is the conservative label retention mode.
In case it is required that LSR is capable of adapting route variation rapidly, you can
use the liberal label retention mode. In case it is required that a few labels are
saved in LSR, you can use the conservative label retention mode.
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Currently, the Switch 8800 Family series adopt the liberal label retention mode.
LDP Label distribution protocol (LDP) is the signaling control protocol in MPLS, which
controls binding labels and FECs between LSRs and coordinates a series of
procedures between LSRs.
The basic composing unit of MPLS network is LSR (Label Switching Router). It runs
MPLS control protocol and L3 routing protocol, exchanges routing messages with
other LSRs and create the routing table, maps FECs with IP packet headers, binds
FECs with labels, distributes label binding messages, establishes and maintains
label forwarding table.
The network consisting of LSRs is called MPLS domain. The LSR that is located at
the edge of the domain is called edge LSR (LER, Labeled Edge Router). It connects
an MPLS domain with a non-MPLS domain or with another MPLS domain,
classifies packets, distributes labels (as ingress LER) and distracts labels (as egress
LER). The ingress LER is termed as ingress and egress LER as egress.
The LSR that is located inside the domain is called core LSR, which provides
functions such as label swapping and label distribution. The labeled packets are
transmitted along the LSP (Label Switched Path) composed of a series of LSRs.