Multiprotocol Lable Switching (Mpls):
Label-Switched Paths (Lsps)
Label Switched Paths:
A predefined path that makes MPLS work are called Label
Switched Paths. In a MPLS network router exchange MPLS information
to exchange these paths. MPLS is often called a layer 2.5
technology because it shares both routing (layer 3) and
switching (layer 2) characteristics.
a.LDP: MPLS LDP enables the
peer LSR in an MPLS network to exchange label binding information
for supporting hop-by-hop forwarding in an MPLS network.
MPLS LDP provides the means for LSRs to request, distribute,
and release label prefix binding information to peer routers
in a network. LDP enables LSRs to discover potential peers
and to establish LDP sessions with those peers for the purpose
of exchanging label binding information.
MPLS LDP enables one LSR to inform another LSR of the
label bindings it has made. Once a pair of routers communicates
the LDP parameters, they establish a label-switched path
(LSP). MPLS LDP enables LSRs to distribute labels along
normally routed paths to support MPLS forwarding. This method
of label distribution is also called hop-by-hop forwarding.
With IP forwarding, when a packet arrives at a router the
router looks at the destination address in the IP header,
performs a route lookup, and forwards the packet to the
next hop. With MPLS forwarding, when a packet arrives at
a router the router looks at the incoming label, looks up
the label in a table, and then forwards the packet to the
next hop. MPLS LDP is useful for applications that require
hop-by-hop forwarding, such as MPLS VPNs.
b. MPLS VPN: "MPLS" and "VPN"
are two different technology types MPLS is a standards-based
technology used to speed up the delivery of network packets
over multiple protocols -such as the Internet Protocol,
Asynchronous Transport Mode, and Frame-Relay network protocol.
A virtual private network (VPN) uses shared public telecom
infrastructure, such as the Internet, to provide secure
access to remote offices and users in a cheaper way than
an owned or leased line. VPNs are secure because they use
tunneling protocols and procedures such as Layer Two Tunneling
Protocol (L2TP). With those definitions understood, an MPLS
VPN is a VPN that is built on top of an MPLS network, usually
from a service provider, to deliver connectivity between
enterprise office locations.