From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Mon, 26 May 2025 06:43:44 +0000 (+0200)
Subject: doc: mention RFC on interleaved modes
X-Git-Tag: 4.7~12
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6c2ee89970a4bb90464cbdf1f5e504700baafe59;p=thirdparty%2Fchrony.git

doc: mention RFC on interleaved modes

The specification of the interleaved modes is now published as
RFC 9769.
---

diff --git a/doc/chrony.conf.adoc b/doc/chrony.conf.adoc
index 82b3639b..16e4fe88 100644
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -251,11 +251,11 @@ authenticated source to be safely combined with unauthenticated sources in
 order to improve the accuracy of the clock. They can be selected and used for
 synchronisation only if they agree with the trusted and required source.
 *xleave*:::
-This option enables the interleaved mode of NTP. It enables the server to
-respond with more accurate transmit timestamps (e.g. kernel or hardware
-timestamps), which cannot be contained in the transmitted packet itself and
-need to refer to a previous packet instead. This can significantly improve the
-accuracy and stability of the measurements.
+This option enables the interleaved mode of NTP (RFC 9769). It enables the
+server to respond with more accurate transmit timestamps (e.g. kernel or
+hardware timestamps), which cannot be contained in the transmitted packet
+itself and need to refer to a previous packet instead. This can significantly
+improve the accuracy and stability of the measurements.
 +
 The interleaved mode is compatible with servers that support only the basic
 mode. Note that even
diff --git a/doc/faq.adoc b/doc/faq.adoc
index fa1b6add..7c881960 100644
--- a/doc/faq.adoc
+++ b/doc/faq.adoc
@@ -338,10 +338,10 @@ with local NTP server
 server ntp.local minpoll 2 maxpoll 4 polltarget 30 maxdelaydevratio 2
 ----
 
-If your server supports the interleaved mode (e.g. it is running `chronyd`),
-the `xleave` option should be added to the `server` directive to enable the
-server to provide the client with more accurate transmit timestamps (kernel or
-preferably hardware). For example:
+If your server supports the interleaved mode (RFC 9769), e.g. it is running
+`chronyd` version 3.0 or later, the `xleave` option should be added to the
+`server` directive to enable the server to provide the client with more
+accurate transmit timestamps (kernel or preferably hardware). For example:
 
 ----
 server ntp.local minpoll 2 maxpoll 4 xleave
diff --git a/ntp_core.c b/ntp_core.c
index fa6acc34..501ea6db 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -1960,7 +1960,7 @@ process_response(NCR_Instance inst, int saved, NTP_Local_Address *local_addr,
   /* The skew and estimated frequency offset relative to the remote source */
   double skew, source_freq_lo, source_freq_hi;
 
-  /* RFC 5905 packet tests */
+  /* RFC 5905 and RFC 9769 packet tests */
   int test1, test2n, test2i, test2, test3, test5, test6, test7;
   int interleaved_packet, valid_packet, synced_packet;
 
@@ -2024,7 +2024,7 @@ process_response(NCR_Instance inst, int saved, NTP_Local_Address *local_addr,
     pkt_root_dispersion = UTI_Ntp32ToDouble(message->root_dispersion);
   }
 
-  /* Check if the packet is valid per RFC 5905, section 8.
+  /* Check if the packet is valid per RFC 5905 (section 8) and RFC 9769.
      The test values are 1 when passed and 0 when failed. */
   
   /* Test 1 checks for duplicate packet */