What is the meaning of Explicit route in MPLS?

Answer 1

MPLS (MultiProtocol Label Switching) - a standard from the IETF for including routing information in the packets of an IP network. MPLS is used to ensure that all packets in a particular flow take the same route over a backbone. Deployed by many telcos and service providers, MPLS can deliver the quality of service (QoS) required to support real-time voice and video as well as service level agreements (SLAs) that guarantee bandwidth. Large enterprises may also use MPLS in their national networks.

Similar to Cisco's tag switching, an MPLS router attaches labels (tags) containing forwarding information to outgoing IP packets. These "label edge routers" (LERs) sit at the edge of the network and perform the complex packet analysis and classification before the packet enters the core of the network. The routers within the core, known as "label switch routers" (LSRs), quickly examine the label and forward the packet per its directions without having to look up data in tables and compute the forwarding path each time. The edge routers at the receiving end remove the labels.

Following in the tradition of the "dumb network," MPLS enables more decisions to be made at the periphery of the network.

An MPLS Core

Using IP and MPLS in the core, a service provider can offer its customers a virtual private VPN service for IP traffic and guarantee bandwidth for real-time voice and video.

EXPLICIT ROUTE:

As the name itself suggest it is a pre-determined explicit path through the MPLS core. In explicit routing, the route the LSP takes is defined by the ingress node. The path consists of a series of hops defined by the ingress LSR. Each hop can be a traditional interface, an autonomous system, or an LSP. A hop can be strict or loose.

A strict hop must be directly connected (that is, adjacent) to the previous node in the path. A loose hop is not necessarily directly connected to the previous node; whether it is directly connected is unknown.

The sequence of hops comprising an explicit routing LSP may be chosen in either of the following ways:

• Through a user-defined configuration, resulting in configured explicit paths. When you create the explicit route, you must manually configure each hop in the path.
• Through a routing protocol-defined configuration, resulting in dynamic explicit paths. When the routing protocol (IS-IS or OSPF) creates the explicit path, it makes use of the topological information learned from a link state database in order to compute the entire path, beginning at the ingress node and ending at the egress node