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FS#3749 - busybox-ntp failing on specific ISP but ntpd works. #8766

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openwrt-bot opened this issue Apr 22, 2021 · 1 comment
Open

FS#3749 - busybox-ntp failing on specific ISP but ntpd works. #8766

openwrt-bot opened this issue Apr 22, 2021 · 1 comment
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flyspray release/21.02 pull request/issue targeted (also) for OpenWrt 21.02 release

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@openwrt-bot
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barhom:

  • Device: glinet B1300 router
  • Running 21.02

Attached are two pcap files you can open in wireshark.

This issue seems to only affect one Danish ISP, however I think it is worth reporting to see if it can be fixed.
The built in busybox-ntpd does not work (see packet in sysntpd.pcap)

However, if I install ntpdate instead then ntp is able to update (using the same ntp server).
You can see difference in the packets by comparing the two pcap files.

My best bet is that the ISP is blocking specific data in NTPv4 Packets that busybox-ntp is sending.

@aparcar aparcar added the release/21.02 pull request/issue targeted (also) for OpenWrt 21.02 release label Feb 22, 2022
@mlichvar
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What makes the difference is likely the source port of the request, not the UDP payload. The busybox ntpd uses a random port, but ntpdate and the ntp.org ntpd use the port 123. This needs to be fixed in the ISP's firewall.

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flyspray release/21.02 pull request/issue targeted (also) for OpenWrt 21.02 release
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