So let’s have a look at MPLS labels, LSPs, and FECs. So what is one MPLS label?
One MPLS label is basically a field of 32 bit. The first 20 bits are reserved for the label value itself. So 20 bits means we have a value which is in a range of zero to one million and a little bit. But that’s a lot of labels that we can have. Then the next three bits are the experimental bits but they have been renamed more recently to traffic class bits. These bits are solely used for quality of service. Then we have the bottom-of-stack bit, it’s just one bit. If this bit is set, it means that this label is at the bottom of the stack. So basically you will have a stack of labels, it could be one label,