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by oxygen_crisis
102 days ago
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Windows NTP client uses UDP port 123 as both the destination and source port, rather than letting the OS assign an ephemeral source port. Many ISPs (e.g. AT&T Fiber) block UDP traffic with source port 123 to mitigate NTP amplification attacks. Most people won't notice that problem since low-end consumer routers tend to mangle the source port when they perform outbound NAT. The ISP-provided router will generally do this itself until you enable "DMZ+" or "IP Passthrough" or some similarly-named mode, as home networking experts will typically do so they can manage NAT and firewalling on their own devices. If a Windows laptop can sync and the wired Windows desktops can't, your wi-fi AP might be doing the necessary source port mangling. If you add a NAT rule to your router to change the source port for NTP traffic, you should get time sync working. |
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