Configuring LDP Session Timers

To configure LDP session timers, use the following command:
configure mpls ldp timers [targeted | link] [{hello-time hello_hold_seconds} {keep-alive-time keep_alive_hold_seconds}]

This command configures the LDP peer session timers for the switch. The LDP peer session timers are separately configurable for link and targeted LDP hello adjacencies.

The hello-time hello_hold_seconds parameter specifies the amount of time (in seconds) that a hello message received from a neighboring LSR remains valid. The rate at which hello messages are sent is one third the configured hello-time. If a hello message is not received from a particular neighboring LSR within the specified hello-time hello_hold_seconds then the hello-adjacency is not maintained with that neighboring LSR. Should two peers have different configured hello-time values, they negotiate to use the lower value.

The session keep-alive time keep_alive_hold_seconds parameter specifies the time (in seconds) during which an LDP message must be received for the LDP session to be maintained. The rate at which keep alive messages are sent, provided there are no LDP messages transmitted, is one sixth the configured keep-alive-time. If an LDP PDU is not received within the specified session keep-alive time keep_alive_hold_seconds interval, the corresponding LDP session is torn down. Should two peers have different configured keep-alive-time values, they negotiate to use the lower value.

In the event that two peers have both a link and a targeted hello adjacency, the hello-time values for the two hello adjacencies are negotiated separately. The keep-alive-time value is established based on negotiations occurring when the LDP session is established following the first hello adjacency to be established.

The minimum and maximum values for both the hello-time hello_hold_seconds and keep-alive time keep_alive_hold_seconds are 6 and 65,534, respectively. Changes to targeted timers only affect newly created targeted peers. Disabling and then enabling all VPLS instances causes all current targeted peers to be re-created.

The default values are as follows:

  • link ldp hello-time hello_hold_seconds – 15
  • targeted-ldp hello-time hello_hold_seconds – 45
  • link ldp hello-time interval_time – auto set to 1/3 the configured hello-time
  • targeted-ldp hello-time interval_time – auto set to 1/3 the configured hello-time
  • link ldp keep-alive keep-alive hold-seconds – 40
  • targeted-ldp keep-alive keep-alive hold-seconds – 60
  • link ldp keep-alive interval_time – auto set to 1/6 the configured keep-alive time
  • targeted-ldp keep-alive interval_time – auto set to 1/6 the configured keep-alive time