Lsp Establishment Procedure - Zte ZXR10 8900 Series User Manual

ZXR10 8900 Series User Manual (MPLS Volume)
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Topology-based drive is to distribute labels for corresponding
routes of routing protocols. When a LSR deals with route up-
date of OSPF or BGP, the LSR modifies the entries in label for-
warding table, meanwhile the LSR distributes labels for these
entries. As long as there is a route, the label for this route is
distributed. Therefore, there is no time delay when LSR for-
wards packets. This mode is widely used.
� Application-based
In this mode, LSR distributes labels according to control service
traffic with normal requirements. The corresponding protocol
is RSVP. When a LSR deals with RSVP, the LSR modifies the en-
tries in label forwarding table, meanwhile the LSR distributes
labels for these entries. This mode requires application pro-
grams bring forward label request and stream rule in advance
to obtain labels. It also distributes labels for existed routes,
so there is no time delay. However, it is difficult to implement
RSVP in the whole network, so this mode is seldom used.
Comparing with packet-based drive, topology-based drive has the
following advantages:
� Label distribution corresponds to control message, therefore,
network cost is little.
� Label is distributed before traffic arrives, so there is no time
delay.
The protocols used to distribute labels for LSRs are called signalling
protocols. Common signalling protocols include:
� Label Distribution Protocol (LDP)
� Constrained Route LDP (CR-LDP)
� Resource Reservation Protocol - Traffic Extension (RSVP-TE)
� Multiprotocol BGP (MP-BGP)

LSP Establishment Procedure

In a MPLS domain, LSP establishment procedure is described as
follows:
1. Each node runs dynamic routing protocols such as BGP,
and IS-IS to generate a routing table.
2. According to the routing table, each node establishes a Label
Information Base (LIB) under the control of LDP.
3. Out labels and in labels from ingress LSR to egress LSR are
mapped to form a LSP.
The detailed procedure is described as follows:
As shown in Figure 8, each router runs OSPF to generate a routing
table. RA, RB and RC learn the route 47.1.0.0/16 to LER.
OSPF