This page discusses enabling MPLS LDP on a Junos device.


  • For LDP to operated on an interface, MPLS family has to be enabled on the logical interface.
  • LDP installs LSPs only when both LDP and the (IGP) routing protocol are enabled. Without it, LDP won't bring up the session.
  • LDP support Basic Discovery and Extended Discovery. Basic, connects to directly connected LDP neighbors, while extended uses targeted hellos.
  • LDP Message Types:
    • Discovery - Discovering neighbors (basic and extended.
    • Session - Session being established via TCP.
    • Advertising - FEC advertising.
    • Notification - Error Notification and Advisory Notification. Error resets session, while advisory just a notification.
  • By default LDP sends Hello message every 5 second for basic discovery (link hello) and 15 seconds for targeted discovery (targeted hello msg).
  • Hello timer and Hello Hold timer is negotiated between LDP peers, where the lowest value wins. These timers are part of the discovery phase.
  • Changing Hello hold timer values requires LDP session restart to allow peers to renegotiate (clear ldp sessions)
  • LDP-signaled LSPs have a preference of 9 vs RSVP-signaled LSPs of 7 (see http://www.juniper.net/techpubs/en_US/junos13.3/topics/reference/general/routing-protocols-default-route-preference-values.html for details). Preference is like Administrative Distance in Cisco.

Relevant Commands

family mpls

set interfaces ae5 unit 0 family inet address
set interfaces ae5 unit 0 family mpls

protocol ldp interface

  • Can be enabled individually or for all interfaces running MPLS and IGP.
set protocol ldp interface ae5.0 
set protocol ldp interface all

protocol ldp interface ae6.0 disable

  • Disables LDP per interface.
set protocol ldp interface ae6.0 disable

protocols ldp interface hello-interval

set protocols ldp interface (int) hello-interval 5

protocols ldp targeted-hello hello-interval

set protocols ldp targeted-hello hello-interval 10

protocols ldp targeted-hello hold-time

set protocols ldp targeted-hello hold-time (value)

protocols ldp interface hold-time

set protocols ldp interface (int) hold-time (value)


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