What is MPLS and its Challenges

From some years customers are changing their legacy FR , ATM , X.25 , LL with Ethernet MPLS Point to Point and multipurpose circuits and MPLS IP VPN . Companies preference of WAN is decided by many factors like Applications , the number of sites , the amount of control on routing decisions , Capacity and one of most important factor is $$$ . Stats  from Telephotography Global Enterprise Networks Research Service propose that one of the main factor influencing an organization’s international network choice may simply be availability.

Biggest challenge to Deploying Right Strategies

One of the biggest challenges are deploying the right strategies and expertise to build , maintain and run an MPLS network . Ethernet VPN Circuits are cost effective than MPLS IP VPN circuits for capacity requirements above 100 Mbps. There is always a need for quick proactive and reactive approach whenever there is a problem in the MPLS network .

It is a good time to know how MPLS works and the troubleshooting . Its all mechanics and not magic , so we need to be good at logic and understanding . Lets help you out over here.

Mpls Ways of Working

Multiprotocol Label Switching (MPLS) mechanism is used in communication networks which deploys short labels instead of longest prefix match for switching network traffic, thus reducing switching delays. MPLS can be considered as layer 2.5 protocol of the standard OSI network model i.e., it operates below the IP layer and on top of the link layer. MPLS enables the transfer IP data over the non IP MPLS networks. Routers at the edges of the MPLS core are called Label Edge Router (LER) and the routers inside the MPLS network are called Label Switch Router (LSR). LERs are, ingress/egress (ingress refers to entrance into Label Switch Path (LSP) and egress refers to exit from the LSP) routers, responsible for attaching the labels to the packets entering the MPLS network and remove the label from the exiting packets. LSRs are the routers which do the traffic forwarding on the basis of label instead of logical 32 bit address.

In the following example R1 is ingress, R3 and R4 are egress LERs and R2 is LSR. In MPLS every router will share with its neighbor the label which has to be attached for a particular IP prefix. Following are the tables of the four routers shown in the figure. Routers R3 and R4 tell R2 that it has to attach a label of 27 for the traffic destined to reach 10.1.1 network and 33 for the traffic destined to reach 10.3.3 network. The “Interface” entry of the label in the forwarding tables shows the interface on which router will transmit the data. Likewise R2 also tells R1 to either append the label of 8 for 10.1.1 network bound traffic or the label of 9 for 10.3.3 network bound traffic. We notice that there is additional entry of “Remote Label” in the forwarding table of R2. Out of the two remote labels (27 & 33) one will be appended to the outgoing traffic depending upon the destination. Like wise R2 also advertises to R1 the labels (“Remote Label” entry in forwarding table of R1) which it should append to outgoing traffic depending upon the destination.

On R2

On R1

On R3

On R4

So next time you face some issues in the forwarding be sure to check labels running in your Network .

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