Microsoft Exchange On-Premise Coexistence Issues Related to Time
Time is a big deal. You have a routine where you wake up, you shower, you have your coffee, and you commute to work. You have meetings throughout the day with multiple people involved all coordinating their own time and their own schedules. Time is important.
Time is no less important for computers. Computers use a protocol called NTP (network time protocol) that synchronizes its own clock with another device’s clock. If computers are joined to a domain, they typically will synchronize with the Active Directory Domain Controller that holds the PDC (primary domain controller) role, as it advertises itself as being a reliable source for time. It is extremely important for this server functioning as the PDC to be a reliable source for time.
It must be:
- Not set to synchronize against itself.
- If it is a virtual machine, it must not be set to synchronize against its host server.
- Set to synchronize against an external reliable time source.
Sikich was recently was engaged to implement an email migration for an on-premise Exchange 2010 server to a new Exchange 2016 server to an environment that we had not worked in previously.
Once I had the Exchange infrastructure built out, mail was not flowing from the Exchange 2010 server to the new Exchange 2016 server. Through troubleshooting, it turns out that the older Exchange 2010 server had been manually set to use an external time source and was dead on for the correct time. However, the new server was set to synchronize with their PDC. The PDC was running 1 minute and 24 seconds slow and was set to synchronize with itself, that is its internal CMOS (complementary metal oxide semiconductor). The CMOS is a battery powered chip that provides information to the computer on boot and they generally hold a charge for many years. However, the clock on this does not synchronize to an external source and therefore is not reliable. Due to a simple 1 minute and 24 seconds, it would prevent email from being sent from one server to another. Time is important.
I generally trust the government for their time, and when in question I visit https://www.time.gov to see what my device clocks should be. When configuring external sources for time I generally trust the servers at http://www.pool.ntp.org. It could be as simple as setting your external sources to these servers:
- 0.pool.ntp.org
- 1.pool.ntp.org
- 2.pool.ntp.org
- 3.pool.ntp.org
Once set, enjoy reliable time across all your domain joined machines.
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