Instruction To Mpls Ldp - Huawei AR1200 Series Configuration Manual - Mpls

Huawei AR1200 Series Enterprise Routers
Configuration Guide - MPLS

2.1 Instruction to MPLS LDP

MPLS LDP, a label distribution protocol, is widely used for transmitting VPN services. Its
networking and configurations are simple. MPLS LDP supports route-driven establishment of
a large number of LSPs.
The IP-based Internet prevailed in the middle 1990s. However, IP technology is inefficient at
forwarding packets because software must search for routes through the longest match algorithm.
As a result, the forwarding capability of IP technology becomes a bottleneck of network
development. The Asynchronous Transfer Mode (ATM) technology has been created from the
evolution of network technologies. It uses labels (particularly, cells) of fixed length and
maintains a label table that is much smaller than a routing table. Therefore, compared to IP
technology, ATM technology is much more efficient at forwarding packets. ATM technology,
however, is a complex protocol with a high cost of deployment, which hinders its widespread
popularity and growth.
Traditional IP technology, however, is simple and costs little to deploy. People are eager to use
technology that combines the best that IP and ATM technologies have to offer. This has sparked
the emergence of Multiprotocol Label Switching (MPLS) technology.
Initially, MPLS was created to increase forwarding rates. With the development of the
application-specific integrated circuit (ASIC) technology Application specific integrated circuit
(ASIC) technology has now been developed, and the routing rate is no longer a bottleneck to
network development. As a result, MPLS no longer has the high-speed forwarding advantage.
MPLS is widely used in virtual private network (VPN), traffic engineering (TE), and quality of
service (QoS) because of its support for multi-layer labels, the connection-oriented forwarding
plane, and the connectionless control plane.
LDP is an MPLS control protocol. Similar to most routing protocols, LDP sends multicast Hello
messages to automatically discover LDP peers and establish peer relationships, or sends unicast
Hello messages to establish target peer relationships. LDP uses negotiated parameters to
establish LDP sessions over TCP connections between peers. LDP sessions send Label Mapping
messages, distribute labels related to routes, and establish LSPs. Data packets travel along the
LSPs over MPLS networks.
In real world situations, LDP is run on the provider (P) devices to forward LDP messages and
on provider edge (PE) devices to support services such as LDP over TE on backbone networks.
Figure 2-1 LDP networking
VPN 1
Issue 01 (2011-12-30)
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VPN 2
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Service provider's
backbone
P P P
P P P
2 MPLS LDP Configuration
VPN 2
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VPN 1
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