[ntp:questions] Is it possible to run ntpd server behind a firewall?

Richard B. Gilbert rgilbert88 at comcast.net
Wed Oct 17 13:23:49 UTC 2007

Shaochun Wang wrote:
> The stupid net administrator of my institute blocked all UDP datagram
> in the firewall. I know that NTP uses UDP to do its work, but is it
> possible to let ntpd use TCP?

No, it's not possible for NTP to use TCP.  UDP was chosen for good
reason; it's a connectionless protocol, does not guarantee delivery and
does no error correction!  These features mean that an NTP packet that
you receive was delivered to you without retransmissions.  This is
important because the NTP algorithms use the transmit and receive time
stamps to determine delay; if you got a new packet with old data in it
it would break ntpd!

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