Chapter 5 Implementing Mpls Traffic Engineering; Implementing Mpls Traffic Engineering - Cisco NCS 5500 Series Configuration Manual

5
C H A P T E R

Implementing MPLS Traffic Engineering

• Implementing MPLS Traffic Engineering, page 37
Implementing MPLS Traffic Engineering
Traditional IP routing emphasizes on forwarding traffic to the destination as fast as possible. As a result, the
routing protocols find out the least-cost route according to its metric to each destination in the network and
every router forwards the packet based on the destination IP address and packets are forwarded hop-by-hop.
Thus, traditional IP routing does not consider the available bandwidth of the link. This can cause some links
to be over-utilized compared to others and bandwidth is not efficiently utilized. Traffic Engineering (TE) is
used when the problems result from inefficient mapping of traffic streams onto the network resources. Traffic
engineering allows you to control the path that data packets follow and moves traffic flows from congested
links to non-congested links that would not be possible by the automatically computed destination-based
shortest path.
Multiprotocol Label Switching (MPLS) with its label switching capabilities, eliminates the need for an IP
route look-up and creates a virtual circuit (VC) switching function, allowing enterprises the same performance
on their IP-based network services as with those delivered over traditional networks such as Frame Relay or
Asynchronous Transfer Mode (ATM). MPLS traffic engineering (MPLS-TE) relies on the MPLS backbone
to replicate and expand upon the TE capabilities of Layer 2 ATM and Frame Relay networks.
MPLS-TE learns the topology and resources available in a network and then maps traffic flows to particular
paths based on resource requirements and network resources such as bandwidth. MPLS-TE builds a
unidirectional tunnel from a source to a destination in the form of a label switched path (LSP), which is then
used to forward traffic. The point where the tunnel begins is called the tunnel headend or tunnel source, and
the node where the tunnel ends is called the tunnel tailend or tunnel destination. A router through which the
tunnel passes is called the mid-point of the tunnel.
MPLS uses extensions to a link-state based Interior Gateway Protocol (IGP), such as Intermediate
System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF). MPLS calculates TE tunnels at
the LSP head based on required and available resources (constraint-based routing). If configured, the IGP
automatically routes the traffic onto these LSPs. Typically, a packet that crosses the MPLS-TE backbone
travels on a single LSP that connects the ingress point to the egress point. MPLS TE automatically establishes
and maintains the LSPs across the MPLS network by using the Resource Reservation Protocol (RSVP).
MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
37