MPLS tutorial

Hi Reader today I am going to Explain you ,

How mpls works in this Mpls tutorial.

Mpls is multiprotocol label switching is mostly found in service provider networks.

MPLS is a technology that is primarily see in the service provider, In service provider networks, the result of using MPLS is that only the routers on the edge of the MPLS domain perform routing lookup; all other routers forward packets based on labels.

MPLS is very useful in service provider (and large enterprise) networks bcoz it enhances BGP routing and provides different services and applications, such as Layer 2 and 3 VPNs, QoS, and TE ( Traffic engineering )

In an MPLS , there are two types of routers:
1) Label-switched router (LSR): A device that forwards packets that are mainly based on
2) Edge LSR: A device that mainly labels packets or forwards IP packets out of an MPLS domain, it? means it is going to be a part of mpls as well as traditional ip routing.

Lets see what is inside MPLS Label ?

mpls tutorial

Field? Description
1. 20-bit label? The actual label used for switching. Values 0 to 15 are reserved.
2. 3-bit experimental (EXP) field? Undefined in the RFC. Used by Cisco to define a class of service (CoS) (IP precedence).
3. Bottom-of-stack bit? MPLS allows multiple labels to be inserted. The bottom-of-stack
bit determines if this label is the last label in the packet. If this bit is set (1), it indicates that this is the last label.
8-bit Time to Live (TTL) field? Has the same purpose as the TTL field in the IP header.

In this snapshot you can see Router receives the ip packet and adds the label ( PUSH ),


Any Router who adds , swap or remove labels are known as LSR ? ( Label Switch Router ),?

Router receives the labeled packet from First Router , and again router is going to check the LFIB and swaps the labeled packet with another label , you can see in above screenshot any? label swapped to label with another label.

Suppose for any prefix label is 25, if its swapped it will be 35.

Now the labeled packet comes to last router , Now Router checks LFIB , A label is removed and the ip packet is sent out to interface .

Now Edge LSR receives the packet and this time it Checks FIB instead of LFIB, Because now we don?t have labels on our packets, and the packet sent to exit interface.

They also looks for FIB ( Forwarding information base ) which works on Traditional IP ,

LFIB ( Label Forwarding information base ) is responsible for Labeling the packets.

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