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| -rw-r--r-- | docs/configuration/service/ntp.rst | 85 |
1 files changed, 84 insertions, 1 deletions
diff --git a/docs/configuration/service/ntp.rst b/docs/configuration/service/ntp.rst index f82baa34..f4ccb4b1 100644 --- a/docs/configuration/service/ntp.rst +++ b/docs/configuration/service/ntp.rst @@ -50,7 +50,7 @@ Configuration * ``time2.vyos.net`` * ``time3.vyos.net`` -.. cfgcmd:: set service ntp server <address> <noselect | nts | pool | prefer> +.. cfgcmd:: set service ntp server <address> <noselect | nts | pool | prefer | ptp | interleave> Configure one or more attributes to the given NTP server. @@ -67,6 +67,12 @@ Configuration this host will be chosen for synchronization among a set of correctly operating hosts. + * ``ptp`` enables the PTP transport for this server (see :ref:`ptp-transport`). + + * ``interleave`` enables NTP interleaved mode (see + `draft-ntp-interleaved-modes`_), which can improve synchronization accuracy + and stability when supported by both parties. + .. cfgcmd:: set service ntp listen-address <address> NTP process will only listen on the specified IP address. You must specify @@ -112,3 +118,80 @@ Configuration timezone. This normally works with the right/UTC timezone which is the default +.. _draft-ntp-interleaved-modes: https://datatracker.ietf.org/doc/draft-ietf-ntp-interleaved-modes/07/ + +Hardware Timestamping of NTP Packets +====================================== + +The chrony daemon on VyOS can leverage NIC hardware capabilities to record the +exact time packets are received on the interface, as well as when packets were +actually transmitted. This provides improved accuracy and stability when the +system is under load, as queuing and OS context switching can introduce a +variable delay between when the packet is received on the network and when it +is actually processed by the NTP daemon. + +Hardware timestamping depends on NIC support. Some NICs can be configured to +apply timestamps to any incoming packet, while others only support applying +timestamps to specific protocols (e.g. PTP). + +When timestamping is enabled on an interface, chrony's default behavior is to +try to configure the interface to only timestamp NTP packets. If this mode is +not supported, chrony will attempt to set it to timestamp all packets. If +neither option is supported (e.g. the NIC can only timestamp received PTP +packets), chrony will leverage timestamping on transmitted packets only, which +still provides some benefit. + +.. cfgcmd:: set service ntp timestamp interface <interface> + + Configures hardware timestamping on the interface <interface>. The special + value `all` can also be specified to enable timestamping on all interfaces + that support it. + + Configure the timestamping behavior with the following option: + + * ``receive-filter [all|ntp|ptp|none]`` selects the receive filter mode, + which controls which inbound packets the NIC applies timestamps to. The + selected mode must be supported by the NIC, or timestamping will be + disabled for the interface. + + +The following `receive-filter` modes can be selected: + +* `all`: All received packets will be timestamped. + +* `ntp`: Only received NTP protocol packets will be timestamped. + +* `ptp`: Only received PTP protocol packets will be timestamped. Combined with + the PTP transport for NTP packets, this can be leveraged to take advantage of + hardware timestamping on NICs that only support the ptp filter mode. + +* `none`: No received packets will be timestamped. Hardware timestamping of + transmitted packets will still be leveraged, if supported by the NIC. + +.. _ptp-transport: + +PTP Transport of NTP Packets +============================= + +The Precision Time Protocol (IEEE 1588) is a local network time synchronization +protocol that provides high precision time synchronization by leveraging +hardware clocks in NICs and other network elements. VyOS does not currently +support standards-based PTP, which can be deployed independently of +NTP. + +For networks consisting of VyOS and other Linux systems running relatively +recent versions of the chrony daemon, NTP packets can be "tunneled" over +PTP. NTP over PTP provides the best of both worlds, leveraging hardware support +for timestamping PTP packets while retaining the configuration flexibility and +fault tolerance of NTP. + +.. cfgcmd:: set service ntp ptp + + Enables the NTP daemon PTP transport. The NTP daemon will listen on the + configured PTP port. Note that one or more servers must be individually + enabled for PTP before the daemon will synchronize over the transport. + +.. cfgcmd:: set service ntp ptp port <port> + + Configures the PTP port. By default, the standard port 319 is used. + |