RFC 9109

Network Time Protocol Version 4: Port Randomization, August 2021

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RFC 5905
F. Gont
G. Gont
M. Lichvar
ntp (int)

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DOI:  https://doi.org/10.17487/RFC9109

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The Network Time Protocol (NTP) can operate in several modes. Some of these modes are based on the receipt of unsolicited packets and therefore require the use of a well-known port as the local port. However, in the case of NTP modes where the use of a well-known port is not required, employing such a well-known port unnecessarily facilitates the ability of attackers to perform blind/off-path attacks. This document formally updates RFC 5905, recommending the use of transport-protocol ephemeral port randomization for those modes where use of the NTP well-known port is not required.

For the definition of Status, see RFC 2026.

For the definition of Stream, see RFC 8729.

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