# MPLS LDP (Label Distribution Protocol) **URL:** https://forum.networklessons.com/t/mpls-ldp-label-distribution-protocol/1285 **Category:** Lessons Discussion **Created:** [December 29, 2016, 8:06pm UTC](https://forum.networklessons.com/t/mpls-ldp-label-distribution-protocol/1285 "2016-12-29T20:06:44Z") **Posts on this page:** 1 **Showing post:** 46
### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis) #### Post date: [April 23, 2019, 7:03am UTC](https://forum.networklessons.com/t/mpls-ldp-label-distribution-protocol/1285/46 "2019-04-23T07:03:17Z")
Hello Jack The case you are describing in your post is penultimate hop popping (PHP), which is a function performed by Label Switch Routers (LSR) before sending the packet to an adjacent Label Edge Router (LER). PHP is achieved because the LER advertises a label with a value of 3 to its neighbors. This is called an implicit-null and it is used for the LERs to inform the LSRs to perform PHP. Rene writes more about this in this post: > [@MPLS Labels and Devices](https://forum.networklessons.com/t/mpls-labels-and-devices/1283/18): > > 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.… I hope this has been helpful! Laz --- _[View the full topic](https://forum.networklessons.com/t/mpls-ldp-label-distribution-protocol/1285)._