NTP Kiss of Death

Kiss-of-Death (KoD) is a feature implemented in the reference implementation of ntpd that is published by ntp.org.

The goal is for an NTP server to be able to send a packet to a client asking the client to reduce the request rate if the client sends requests too frequently.

To enable this feature on an NTP server, the server has to be properly configured using the restrict keywords discard, limited and **kod with appropriate values. See:

• https://www.meinbergglobal.com/download/ntp/docs/html/accopt.html#restrict

However, the effectiveness of this feature is disputed.

• If the client is running benign NTP software, the client won't send queries too frequently anyway,

and the server never needs to send a KoD packet to that client.

• If the NTP client software isn't well behaved anyway, the client will mostly not reduce the request rate even if it gets a KoD packet from the server.

It is therefore generally questionable whether it makes any sense to activate the kiss-of-death feature.

— Martin Burnicki martin.burnicki@meinberg.de, last updated 2022-10-04