BROCADE IP PRIMER

Multi Protocol LabelSwitching (MPLS)12Now we are ready to learn about Multi Protocol Label Switching (MPLS) andhow it can be used in your network.What is MPLS?Let’s take a look at MPLS. MPLS is a highly scalable, protocol agnostic, datacarryingmechanism. In an MPLS network, data packets are assigned labels,and the packet-forwarding decisions are based solely on the contents of thislabel, without the need to examine the packet itself. This allows users to createend-to-end circuits across any type of transport medium, using any protocol.The MPLS label lookup and label switching is faster than the Routing InformationBase as it is performed in the switch fabric and not the CPU.MPLS ConceptsHow does it work? MPLS works by prefixing packets with an MPLS header, containingone or more “labels.” This is called a label stack and each label stackentry contains the following four fields:• A 20-bit label value• A 3-bit Class of Service and Explicit Congestion Notification (ECN)• A 1-bit end of stack• A 8-bit time to live fieldMPLS header32 bits = 4 bytesLabel Value TC S TTL20 bits3 bits 1 8 bitsbitB_392At the edge of the MPLS network, packets are labeled when entering the networkand labels are removed when exiting the network. The labeling of thepacket as it enters the MPLS network is called a push and the removal of thelabel as it exists the network is called a pop. This is performed by the LabelBrocade IP Primer 261