patchlwIP - A Lightweight TCP/IP stack - Patches: patch #9856, sntp: Allow both IPv4 and IPv6 NTP...


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patch #9856: sntp: Allow both IPv4 and IPv6 NTP servers to be configured simultaneously via DHCP

Submitter:  David J. Fiddes <davefiddes>
Submitted:  Sun 29 Sep 2019 05:00:29 PM UTC
Category:  apps Priority:  3 - Low
Status:  None Privacy:  Public
Assigned to:  None Open/Closed:  Open
Planned Release:  None

Tue 10 Dec 2019 10:04:56 PM UTC, comment #2: 

If you're on an IPv4 network you'll get your IPv4 NTP (or DNS) servers via DHCP. If you are on IPv6 you'll get IPv6 NTP servers over DHCP. If you are operating dual-stack you have to deal with both.

I did wonder whether these patches would open a can of worms. Dual stack makes a lot of things ugly unfortunately.

For my own use case ESP8266 Arduino's LwIP configuration has 3 NTP server slots and only 1 DHCP and 1 DHCPv6 NTP server. This works fine obviously.

I'll need to have a think as to how to achieve it but dividing the allocation between IPv4 and IPv6 would certainly be more deterministic.

David J. Fiddes <davefiddes>
Tue 10 Dec 2019 08:55:09 PM UTC, comment #1: 

I could imagine a lot of funny things happen when applying this patch as is. For example, if the number of available slots was smaller than what we get via DHCPv6, we wouldn't be able to store IPv4 servers?

Up to now, the assumption was that networks either give us IPv4 or IPv6 servers.

If that's not the case, maybe separate lists (or fixed offsets in a single list) would be better than this kind of magic?

Simon Goldschmidt <goldsimon>
Project Administrator
Sun 29 Sep 2019 05:00:29 PM UTC, original submission:  

Currently when a DHCP or DHCPv6 updates containing NTP
server addresses is processed all existing NTP server addresses
are wiped. This can lead to problems when there is intermittent
connectivity to an NTP server over a given IP protocol. This
changes DHCP update processing such that it only overwrites
server addresses for the same protocol. It also does the same
for IPv4 NTP server addresses when processing a DHCPv6 update.

The logging for processing DHCP and DHCPv6 updates are now
a bit more useful.

 - On a network with DHCP and DHCPv6 configure differing
   numbers (0-3) of NTP servers on each protocol. Ensure that
   as updates are processed the list of 3 LWIP NTP servers is
   updated as expected.
 - On a network with intermittent IPv6 connectivity ensure that
   with both IPv4 and IPv6 servers configured via DHCP that NTP
   updates are requested over IPv4 even if it is not listed first.

David J. Fiddes <davefiddes>


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  • -email is unavailable- added by goldsimon (Posted a comment)
  • -email is unavailable- added by davefiddes (Submitted the item)

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    Follows 1 latest change.

    Date Changed by Updated Field Previous Value => Replaced by
    2019-09-29 davefiddes Attached File- Added 0001-sntp-Don-t-over-write-IPv6-NTP-server-when-processin.patch, #47586

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