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

[Shaochun Wang]

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