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

Terje Mathisen terje.mathisen at hda.hydro.com
Wed Oct 17 05:58:22 UTC 2007

Shaochun Wang wrote:
> Danny Mayer wrote:
>> 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.  You cannot "let" ntpd use TCP. NTP is a UDP-only protocol. Talk to
>> your net admin. Maybe he can set up a NTP server on the firewall.
>> Danny
> But why the following entry exists in /etc/services file?
> ntp             123/tcp                         # Network Time Protocol

Because 123/tcp was reserved for NTP at the same time as 123/udp!

We've been discussing for years if we should start using 123/tcp for 
things like configuration and monitoring, where you can get _very_ long 

The core ntp protocol will never use 123/tcp however.


- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"

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