Solved

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

Posted on 2008-10-15
4
9,940 Views
Last Modified: 2013-12-16
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.
0
Comment
Question by:tballah
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
4 Comments
 
LVL 10

Expert Comment

by:Pétur Ingi Egilsson
ID: 22720880
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.
0
 
LVL 10

Expert Comment

by:Pétur Ingi Egilsson
ID: 22720898
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.
0
 
LVL 1

Author Comment

by:tballah
ID: 22732931
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?
0
 
LVL 10

Accepted Solution

by:
Pétur Ingi Egilsson earned 250 total points
ID: 22732961
use `netstat -na|grep LISTEN` to see if anything is listening on the 123/TCP

As i stated.. 123/TCP is only listed in /etc/services as a reservation...
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Little introduction about CP: CP is a command on linux that use to copy files and folder from one location to another location. Example usage of CP as follow: cp /myfoder /pathto/destination/folder/ cp abc.tar.gz /pathto/destination/folder/ab…
Creating an OSPF network that automatically (dynamically) reroutes network traffic over other connections to prevent network downtime.
Learn how to get help with Linux/Unix bash shell commands. Use help to read help documents for built in bash shell commands.: Use man to interface with the online reference manuals for shell commands.: Use man to search man pages for unknown command…
Connecting to an Amazon Linux EC2 Instance from Windows Using PuTTY.

688 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question