312-50V11 · Question #136
You perform a scan of your company's network and discover that TCP port 123 is open. What services by default run on TCP port 123?
The correct answer is C. Network Time Protocol. Port 123 is assigned to the Network Time Protocol (NTP), which synchronizes clocks across network devices.
Question
You perform a scan of your company's network and discover that TCP port 123 is open. What services by default run on TCP port 123?
Options
- ATelnet
- BPOP3
- CNetwork Time Protocol
- DDNS
How the community answered
(26 responses)- A4% (1)
- B4% (1)
- C88% (23)
- D4% (1)
Why each option
Port 123 is assigned to the Network Time Protocol (NTP), which synchronizes clocks across network devices.
Telnet uses TCP port 23, not port 123, and provides unencrypted remote terminal access.
POP3 (Post Office Protocol v3) uses TCP port 110 for retrieving email from a mail server.
NTP is assigned to port 123 by IANA and is used to synchronize system clocks over IP networks. While NTP most commonly operates over UDP 123, TCP 123 is also part of the same port assignment. Discovering TCP 123 open suggests an NTP service or a service using that registered port is running on the host.
DNS primarily uses UDP port 53 (and TCP 53 for zone transfers and large responses), not port 123.
Concept tested: Well-known port number assignments
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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