Maximum tolerance for computer clock synchronization

A brief look at configuring Maximum tolerance for computer clock synchronization

This security setting determines the maximum time difference expressed in minutes that Kerberos V5 tolerates between the time on the client clock and the time on the domain controller that provides Kerberos authentication.

Security concerns:

The Kerberos v5 protocol uses time stamps as part of its protocol definition for authenticating connection requests. This prevents "replay attacks". A replay attack is an unauthorized storage of data that is re-transmitted to trick users into performing harmful operations. The clocks of the client and the domain controller need to be in sync as much as possible for accurate time-stamp readings. Since there will always be some minor time differences between both clocks, you can use the Maximum tolerance for computer clock synchronization policy setting to establish the maximum acceptable difference between a client clock and domain controller clock.

If the difference between a client computer clock and the domain controller clock is less than the maximum time difference that is specified in this policy, any time stamp that is used in a session between the two devices is considered to be authentic.

The policy setting can take values from 1 through 99,999 or can be left undefined.

The Microsoft recommended value is 5 minutes. This is generally the default value.

Enabling the policy setting:

Client devices receive a fresh configuration when the next scheduled and successful Group Policy refresh occurs. To enforce these new settings, you'll need to run the following command in a prompt: gpupdate.exe /force. On the local device, the Security Configuration Engine will refresh this setting in about five minutes.

Settings are applied in the following order through a Group Policy Object (GPO), which will overwrite settings on the local computer at the next Group Policy update:

• Local policy settings
• Site policy settings
• Domain policy settings
• OU policy settings

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