MPLS LDP (Label Distribution Protocol)

[lagapidis (Lazarus Agapidis)]

Hello Giovanni

Take a look at this post which further explains the implicit and explicit NULL labels:

MPLS Labels and Devices

Hi Kumaran, These have to do with PHP (Penultimate Hop Popping). Imagine you have a couple of routers like this: CE1 - PE1 - P1 - P2 - PE2 - CE2 Let’s say CE1 sends an IP packet meant for CE2. What happens is that PE1 adds a label and then it gets label switched from PE1 to P1 > P2 > PE2. To save PE2 a label lookup, we use PHP. This means that P2 will remove the label before forwarding it to PE2. This will save PE2 a label lookup. P2 knows that it has to do PHP because PE2 will tell it to.…

Also, take a look at these two NetworkLessons notes on the topic:

• MPLS implicit NULL
• MPLS explicit NULL

I hope this has been helpful!

Laz