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Delaying Preemption

September 21, 2020
Contributed by: 
C

By default, a backup VIP address preempts the master VIP address immediately after its priority becomes higher than that of the master VIP. When configuring a backup VIP address, you can specify an amount of time by which to delay the preemption. Preemption delay time is a per-node setting for each backup VIP address.

The preemption delay setting for a backup VIP does not apply in the following conditions:

  • The node of the master VIP goes down. In this case, the backup VIP takes over as the master VIP after the dead interval set on the backup VIP’s node.
  • The priority of the master VIP is set to zero. The backup VIP takes over as the master VIP after the dead interval set on the backup VIP’s node.

Example: Delaying Preemption

Consider an active-active deployment consisting of Citrix ADC appliances NS1 and NS2. Virtual IP address VIP1 is configured on each of these appliances. Because of their priorities, VIP1 is master on NS2. Preemption is enabled and preemption delay time is set for VIP1 on these two nodes.

The following table lists the settings used in this example.

Entity and Parameters Settings on NS1 Settings on NS2
VIP1 (for reference purposes only) IP address: 192.0.1.10, VRID: 10, Priority: 100, Preemption: Enabled, Preemption delay time: 1000 seconds IP address: 192.0.1.10, VRID: 10, Priority: 200, Preemption: Enabled, Preemption delay time: 2000 seconds
Dead Interval 1 Seconds 2 Seconds

Following are some examples of possible preemption behavior in this setup:

  • If the priority of VIP1 on NS1 is set to a value (for example, 210) higher than that of VIP1 on NS2, VIP1 on NS1 takes over as master after its set preemption delay time (1000 secs).
  • If a third node NS3 with the following VRRP settings is added to this deployment, VIP1 on NS3 becomes master after its set preemption delay time (3000 secs).
    • VIP1
      • VRID: 30
      • IP address:
      • Priority = 300
      • Preemption delay time = 3000 seconds
  • If NS2 goes down, VIP1 on NS1 takes over as master after 1 second (set dead interval on NS1). Preemption delay time for VIP1 on NS1 does not apply in this case.
  • If NS2 goes down and NS1 restarts, VIP1 on NS1 becomes master 1 second (set dead interval on NS1) after NS1 comes up. Preemption delay time for VIP1 on NS1 does not apply in this case.
  • If the priority of VIP1 on NS2 is set to zero, VIP1 goes to standby mode. VIP1 on NS1 takes over as master after 1 second (set dead interval on NS1). Preemption delay time for VIP1 on NS1 does not apply in this case.

Configuring Delay Preemption for IPv4 Active-Active Mode

To configure preemption delay time for a VIP address, you set the preemption delay timer parameter of the associated Virtual MAC address. You can the set this parameter when you add the address, or you can modify an existing Virtual MAC address.

To configure preemption delay time by using the CLI:

  • To set the preemption delay time while adding a Virtual MAC, at the command prompt, type:
    • add vrID <id> -preemptiondelaytimer <secs>
    • show vrID
  • To set the preemption delay time while modifying a Virtual MAC, at the command prompt, type:
    • set vrID <id> -preemptiondelaytimer <secs>
    • show vrID

To configure preemption delay time by using the GUI:

  1. Navigate to System > Network > VMAC.
  2. On the VMAC tab. While adding a new Virtual MAC, or editing an existing Virtual MAC, set the Preemption Delay Timer parameter.

Sample configuration:

The following configuration uses the settings listed in table in section Example: Delaying Preemption.

    Settings on NS1

    > set vrid param –deadInterval 1

    Done

    > add ns ip 192.0.1.10 255.255.255.255 –type VIP

    Done

    > add vrid 10 –Priority 100 –Preemption Enable –preemptiondelaytimer 1000

    Done

    > bind ns ip 192.0.1.10 255.255.255.255 –vrid 10

    Done

    Settings on NS2

    > set vrid param –deadInterval 2

    Done

    > add ns ip 192.0.1.10 255.255.255.255 –type VIP

    Done

    > add vrid 20 –Priority 200 –Preemption Enable –preemptiondelaytimer 2000

    Done

    > set ns ip 192.0.1.10 255.255.255.255 –vrid 10

    Done

Configuring Delay Preemption for IPv6 Active-Active Mode

To configure preemption delay time for a VIP6 address, you set the preemption delay timer parameter of the associated Virtual MAC6 address. You can the set this parameter when you add the Virtual MAC6 address, or you can modify an existing Virtual MAC6 address.

To configure preemption delay time by using the CLI:

  • To set the preemption delay time while adding a Virtual MAC6, at the command prompt, type:
    • add vrID6 **<id> -preemptiondelaytimer** <secs>
    • show vrID6

  • To set the preemption delay time while modifying a Virtual MAC6, at the command prompt, type:

    • set vrID6 <id> -preemptiondelaytimer <secs>
    • show vrID6

To configure preemption delay time by using the GUI:

  1. Navigate to System > Network > VMAC.
  2. On the VMAC6 tab. While adding a Virtual MAC6 address, or editing an existing Virtual MAC6 address, set the Preemption Delay Timer parameter.
Delaying Preemption
September 21, 2020
Contributed by: 
C
September 21, 2020
Contributed by: 
C

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