Oct 25 2008
MPLS Header
This is what an MPLS label looks like. The MPLS label contains a 20-bit label, dont get confused between the different uses of the word label.
The 3 bit EXP bits are used for QoS purposes. You can use them to define different tunnel modes, which I’ll talk about on another day.
The S bit identifies the bottom label of the stack.
The TTL field is similar to the IP TTL, ie if the MPLs TTL reaches zero the MPLS frame is discarded.
The MPLS frame is inserted between the layer 2 frame header and the layer 3 header.
Click here if you want to see a powerpoint version of the MPLS frame header
