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ntp/tcp is listed as a reserved port for ntp.<br />
Does not mean anything is listening on it.<br />
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It would confuse people if you would have different reserved ports for both the TCP and UDP protocols.<br />

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ntp/tcp is listed as a reserved port for ntp.
Does not mean anything is listening on it.

It would confuse people if you would have different reserved ports for both the TCP and UDP protocols.


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example:<br />
port 80 TCP is reserved for HTTPd<br />
It would be confusing if you had port 80 TCP for HTTPd and port 80 UDP running something completely diffrent.
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example:
port 80 TCP is reserved for HTTPd
It would be confusing if you had port 80 TCP for HTTPd and port 80 UDP running something completely diffrent.

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I know a bit from DNS service that it uses port 53/UDP for query and 53/TCP for zone transfer between primary and secondary DNS server. I was thinking the same way for NTP service as defined in /etc/services. By the way who could I know the nature of the service whether it is pure UDP or TCP?
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I know a bit from DNS service that it uses port 53/UDP for query and 53/TCP for zone transfer between primary and secondary DNS server. I was thinking the same way for NTP service as defined in /etc/services. By the way who could I know the nature of the service whether it is pure UDP or TCP?

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I check from /etc/services and I find that there are 2 lines for ntp services:<br />
ntp &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 123/tcp<br />
ntp &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 123/udp<br />
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I got an answer from EE expert that I cannot telnet to NTP server using port 123 as it is UDP. I wonder when TCP is used for NTP service.
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I check from /etc/services and I find that there are 2 lines for ntp services:
ntp             123/tcp
ntp             123/udp

I got an answer from EE expert that I cannot telnet to NTP server using port 123 as it is UDP. I wonder when TCP is used for NTP service.

When UDP is used for NTP service and when TCP is used for NTP service?

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Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of networking protocols that define end-to-end connectivity specifying how data should be packeted, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.