[Ntp] Re: [EXT] [EXT] Focussing loop detection on loop detection only.

["Windl, Ulrich" <[e-mail]>]

Hi!

I'm missing the argument WHY it's possible to "remove the need for stratum 1 servers".
For example a stratum-1 server using a DCF77 clock as reference may become a stratum-2 server during thunderstorms when the sender is switched off, or when receptions is barely possible.

Kind regards,
Ulrich Windl

> -----Original Message-----
> From: David Venhoek <david=[e-mail]>
> Sent: Wednesday, July 8, 2026 9:54 AM
> To: NTP WG <[e-mail]>
> Subject: [EXT] [EXT] [Ntp] Focussing loop detection on loop detection only.
> 
> 
> Hi All,
> 
> As an alternative to Miroslav's weighted list idea for loop detection,
> I want to propose we improve the capacity of the bloom filter by
> removing a lot of the unnecessary sources from the bloom filter
> itself. Removing the need for stratum 1 servers to put anything in the
> bloom filter removes a large number of identifiers, reducing the
> number of ids in miroslav's 5 strata example from 3906 back down to a
> much more managable 626.
> 
> The desire to provide information on where the time is coming from
> primarily can be solved separately by including something similar (but
> a bit more robust) to the ntpv4 reference id. This can provide
> information on the primary source of the server, IF the server is
> willing to share it. Making it optional allows servers which want to
> have a more defensive posture to not provide such information without
> having to mess with the loop detection mechanism and becoming
> non-compliant.
> 
> Patches to the specification providing these changes are included
> below, and in the following PR on github:
> https://github.com/ietf-wg-ntp/draft-ietf-ntp-ntpv5/pull/32
> 
> Kind regards,
> David Venhoek
> 
> >From 685bd47204650e2be7fc132de1d1c15fec9cb204 Mon Sep 17 00:00:00
> 2001
> From: David Venhoek <[e-mail]>
> Date: Wed, 8 Jul 2026 09:18:08 +0200
> Subject: [PATCH 1/2] Remove information on non-ntpv5 sources from bloom
>  filter.
> 
> This provides more room in the bloom filter for sources for which loop
> detection is actually needed, extending the useful capacity of the
> filter.
> ---
>  ntp-ntpv5.xml | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/ntp-ntpv5.xml b/ntp-ntpv5.xml
> index 0c51aef..ead2c3d 100644
> --- a/ntp-ntpv5.xml
> +++ b/ntp-ntpv5.xml
> @@ -769,15 +769,11 @@
>            sources selected for synchronization and the server's own reference
>            ID.</t>
> 
> -        <t>If the server uses a previous version of NTP for some of its
> -          sources, the reference IDs added to the filter are generated from
> -          their IP addresses as the first 120 bits of the
> -          <xref target="RFC1321">MD5</xref> sum of the address in network
> -          order. If the server uses a reference clock, the reference ID is the
> -          first 120 bits of the MD5 sum of the 4-octet zero-padded ASCII
> -          string from the NTP Reference Identifier Codes registry maintained by
> -          IANA, or a string beginning with the uppercase letter X, which are
> -          reserved for private and experimental use.</t>
> +        <t>Sources the server uses that are not using NTPv5 shall not
> be included
> +          in the bloom filter. Furthermore, a server not considering any NTPv5
> +          server as a potential source may choose to send an empty bloom filter
> +          to its clients. This provides more room in the bloom filter
> for downstream
> +          clients, lowering the probability of false positives.</t>
> 
>          <t>A client checking whether the server's set of reference IDs contains
>            the client's own reference ID checks whether the bits at the 10
> --
> 2.47.3
> 
> >From 59095c3a611cea5791c6a10d25c1235f02302526 Mon Sep 17 00:00:00
> 2001
> From: David Venhoek <[e-mail]>
> Date: Wed, 8 Jul 2026 09:19:15 +0200
> Subject: [PATCH 2/2] Provide an optional mechanism for indicating the
> primary
>  time source.
> 
> This allows servers to provide insight into what their primary source of
> synchronization is, without having to use valuable space in the bloom
> filter and without risks of false positives.
> ---
>  ntp-ntpv5.xml | 97
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
> 
> diff --git a/ntp-ntpv5.xml b/ntp-ntpv5.xml
> index ead2c3d..608c349 100644
> --- a/ntp-ntpv5.xml
> +++ b/ntp-ntpv5.xml
> @@ -881,6 +881,56 @@
>            to other NTP servers (i.e. they can be in a synchronization
> loop).</t>
>        </section>
> 
> +      <section title="Primary Source Extension Field"
> +          anchor="primary-source-extension-field">
> +        <t>This extension filed provides a method for clients to query a server
> +          about what its most important source of time
> synchronization is. It consists
> +          of a Kind field describing the kind of identifier, together
> with the actual
> +          value of the source identifier.</t>
> +
> +        <t>The format of the Primary Source Extension Field is shown
> in Figure <xref
> +          format="counter" target="primary-source-ext-field"/>.</t>
> +
> +        <figure align="center" anchor="primary-source-ext-field"
> +            title="Format of Primary Source Extension Field">
> +          <artwork><![CDATA[
> + 0                   1                   2                   3
> + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +| Type = [[TBD]] (draft 0xF50A) |             Length            |
> ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +|      Kind     |    Reserved   |                               |
> ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
> +.                                                               .
> +.                   Source Identifier (variable)                .
> +.                                                               .
> ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> +          ]]></artwork>
> +        </figure>
> +
> +        <t>The client requests information on the primary source of a server by
> +          including the Primary Source Extension Field in its
> request, with special None kind (0)
> +          and a identifier 16 bytes long consisting of all 0s. The
> dummy value is provided to
> +          ensure there is room for the identifier in the response
> regardless of its kind.</t>
> +
> +        <t>If supported by the server, and if the identifier is
> shorter or equal in length to the
> +          None identifier provided by the client, the server SHALL
> include a Primary Source Extension
> +          Field in its response containing the source identifier of
> the source which most
> +          contributes to its estimate of the current time. The server
> SHALL NOT send a Primary Source
> +          Extension Field in its response which is larger than the
> Primary Source Extension Field in the
> +          client's request.</t>
> +
> +        <t>If the servers primary source is an NTP source reached
> over IpV4, it shall use the IpV4 kind (1)
> +          and provide the IpV4 address of the source as the source
> identifier.</t>
> +
> +        <t>If the servers primary source is an NTP source reached
> over IpV6, it shall use the IpV6 kind (2)
> +          and provide the IpV6 address of the source as the source
> identifier.</t>
> +
> +        <t>If the servers primary source cannot reasonably be
> described by any of the other kinds known to
> +          the server, it may use the NTP Reference Identifer kind
> (3), and provide an entry from the IANA NTP Reference
> +          Identifier Codes table to describe the source.</t>
> +      </section>
> +
>        <section title="Server Information Extension Field"
>            anchor="server-information-extension-field">
>          <t>This field provides clients with information about which NTP
> @@ -1732,6 +1782,10 @@ Tx  | 0  |    | t3'|      | 0  |    | t3 |
> | 0  |    |t11'|
>          <c>Reference IDs Request</c>
>          <c><xref target="reference-ids-extension-fields">[[this
> memo]]</xref></c>
> 
> +        <c>[[TBD]]</c>
> +        <c>Primary Source</c>
> +        <c><xref target="primary-source-extension-field">[[this
> memo]]</xref></c>
> +
>          <c>[[TBD]]</c>
>          <c>Reference IDs Response</c>
>          <c><xref target="reference-ids-extension-fields">[[this
> memo]]</xref></c>
> @@ -1774,6 +1828,49 @@ Tx  | 0  |    | t3'|      | 0  |    | t3 |
> | 0  |    |t11'|
>          <c>Network Time Protocol version 5 (NTPv5)</c>
>          <c><xref target="network-time-security">[[this memo]]</xref></c>
>        </texttable>
> +
> +      <t>IANA is requested to create a new registry entitled "Network Time
> +        Protocol Source Identifier Types". Its entries SHALL have the following
> +        fields:
> +        <list>
> +          <t>Number (REQUIRED): An integer in the range 0&ndash;255
> inclusive.</t>
> +          <t>Description (REQUIRED): A short text description of the
> identifier type.</t>
> +          <t>Reference document (REQUIRED): A reference to the relevant
> +            specification document.</t>
> +        </list>
> +        The policy for allocation of new entries in this registry SHALL vary by
> +        their Number, as follows:
> +        <list>
> +          <t> 0&ndash;247: IETF Review</t>
> +          <t> 248&ndash;255: Private and Experimental Use</t>
> +        </list>
> +      </t>
> +
> +      <t> The initial contents of the Network Time Protocol Source
> Identifier Types
> +        Registry SHALL be as follows:
> +      </t>
> +
> +      <texttable>
> +        <ttcol>Number</ttcol>
> +        <ttcol>Description</ttcol>
> +        <ttcol>Reference</ttcol>
> +
> +        <c>0</c>
> +        <c>None</c>
> +        <c><xref target="primary-source-extension-field">[[this
> memo]]</xref></c>
> +
> +        <c>1</c>
> +        <c>IpV4</c>
> +        <c><xref target="primary-source-extension-field">[[this
> memo]]</xref></c>
> +
> +        <c>2</c>
> +        <c>IpV6</c>
> +        <c><xref target="primary-source-extension-field">[[this
> memo]]</xref></c>
> +
> +        <c>3</c>
> +        <c>NTP Reference Identifier</c>
> +        <c><xref target="primary-source-extension-field">[[this
> memo]]</xref></c>
> +      </texttable>
>      </section>
> 
>      <section title="Implementation Status - RFC EDITOR: REMOVE BEFORE
> PUBLICATION">
> --
> 2.47.3
> 
> _______________________________________________
> ntp mailing list -- [e-mail]
> To unsubscribe send an email to [e-mail]