Mpls And Routing Protocols; Applications Of Mpls - 3Com S7906E Configuration Manual

Structure of an LSR
Figure 1-5 Structure of an LSR
As shown in Figure
Control plane: Implements label distribution and routing, establishes the LFIB, and builds and tears
LSPs.
Forwarding plane: Forwards packets according to the LFIB.
An LER forwards both labeled packets and IP packets on the forwarding plane and therefore uses both
the LFIB and the FIB. An ordinary LSR only needs to forward labeled packets and therefore uses only
the LFIB.

MPLS and Routing Protocols

When establishing an LSP hop by hop, LDP uses the information in the routing tables of the LSRs along
the path to determine the next hop. The information in the routing tables is provided by routing protocols
such as IGPs and BGP. LDP only uses the routing information indirectly; it has no direct relationship
with routing protocols.
On the other hand, existing protocols such as BGP and RSVP can be extended to support label
distribution.
In MPLS applications, it may be necessary to extend some routing protocols. For example,
MPLS-based VPN applications requires that BGP be extended to propagate VPN routing information,
and MPLS-based Traffic Engineering (TE) requires that OSPF or IS-IS be extended to carry link state
information.

Applications of MPLS

By integrating both Layer 2 fast switching and Layer 3 routing technologies, MPLS features improved
route lookup speed. However, with the development of the application specific integrated circuit (ASIC)
technology, route lookup speed is no longer the bottleneck hindering network development. This makes
MPLS not so outstanding in improving forwarding speed.
1-5, an LSR consists of two planes:
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