NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38.

ntp-4.2.8p15 was released on 23 June 2020. It addresses 1 medium-severity security issue in ntpd, and provides 13 non-security bugfixes over 4.2.8p13.

Please see the NTP Security Notice for vulnerability and mitigation details.

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Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.

Kiss-o'-Death (KOD) Responses

Related Topics: NtpProtocolResponseMatrix

KOD codes and meanings

Per RFC5905, Section 7.4 and Figure 13.

DENY - Access denied by remote server

The client MUST demobilize any associations to that server and stop sending packets to that server.

Question: For how long?

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RATE - Rate exceeded. The server has temporarily denied access because the client exceeded the rate threshold.

The client MUST immediately reduce its polling interval to that server and continue to reduce it each time it receives a RATE kiss code.

Question: How long before the client might try and ask more frequently?

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RSTR - Access denied due to local policy

The client MUST demobilize any associations to that server and stop sending packets to that server.

Question: For how long?

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X***

These codes are unregistered and experimental codes. Unless your implementation recognizes the particular code, it MUST be ignored.

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"For how long"?

What are good numbers for how long one should "back off" after a KOD response? "Forever" seems way too long. This is similar to the question of "how long should we use an IP we got from a DNS name before we re-resolve it?" In this latter case, Harlan can easily see the case where the TTL value is likely "too short". But that's a different question for a different topic...

• Perhaps it could be a function of the ppoll value from the received KOD packet with some hard-coded minimum and maximum? -- MiroslavLichvar - 28 Jan 2014

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Is the KOD mechanism really useful?

• For enforcement, no. As an advisory mechanism, certainly. Think of them as an error return code from any other type of request. -- BrianUtterback - 22 Jan 2014

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