Leveraging the "iburst" Option for Faster ESXi Time Synchronization with NTP

Products

• VMware vSphere ESXi 7.0
• VMware vSphere ESXi 8.0

Issue/Introduction

This kb helps in configuring the "iburst" option in NTP on the ESXIs to speed up the sync process of the time synchronization with NTP protocol. 

Environment

vSphere 7, 8 

VCF 4.x, 5.x 

Cause

The customer might require NTP to synchronize faster for multiple purposes: 

• For Automation of the ESXI deployment through scripted methods, 
• For faster time sync on the time-sensitive Application VMs syncing time from the ESXi 

By default, the ESXi takes approximately up to 200 seconds to sync time with the NTP server

This is can observed in the following manner: 

Note: The examples on this KB use Google's time server. However, the behavior is consistent across all the time server configurations using the NTP protocol. 

• Configure the NTP: 

            esxcli ntp set -r time1.google.com

• Now watch the status of the NTP sync 

           watch esxcli system ntp get

• The initial output will look like the following: 

 Enabled: true
  Loglevel: warning
  PID: 1171389
  Runtime Seconds: 2
  Servers: time1.google.com 
  Service Providing Kernel Time: Network Time Protocol
  Time Service Enabled: true
  Time Synchronized: false

• When the time reaches roughly 200 seconds we will see that the time sycn is done.   

 Enabled: true
  Loglevel: warning
  PID: 1171389
  Runtime Seconds: 190
  Servers: time1.google.com,  
  Service Providing Kernel Time: Network Time Protocol
  Time Service Enabled: true
  Time Synchronized: true

Resolution

Configuring "iburst": 

• To fasten the time sync process we can add the iburst parameter along with the NTP server.

     esxcli system ntp set -s 'time1.google.com iburst' 

• Watch the get command to see the time taken for the sync. 

watch esxcli system ntp get

   Enabled: true
   Loglevel: warning
   PID: 1171389
   Runtime Seconds: 6
   Servers: time1.google.com iburst
   Service Providing Kernel Time: Network Time Protocol
   Time Service Enabled: true
   Time Synchronized: false

• We can observe that at the 8th second the time sync is complete: 

  Enabled: true
   Loglevel: warning
   PID: 1171389
   Runtime Seconds: 8
   Servers: ntp.broadcom.net iburst, time1.google.com iburst
   Service Providing Kernel Time: Network Time Protocol
   Time Service Enabled: true
   Time Synchronized: true