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Difficulty: HardCommon Ports and Protocols

A network administrator is configuring inbound ACL rules on an edge firewall. The security baseline requires enabling secure, encrypted command-line management for distant switches while allowing internal infrastructure devices to synchronize their clocks against an external stratum-1 time server. Which TWO of the following port and transport protocol combinations must be permitted in the firewall policy? (Select TWO)

  1. TCP port 22Answer
  2. UDP port 123Answer
  3. C
    TCP port 23
  4. D
    TCP port 123

Answer

The required services are Secure Shell (SSH), which operates over TCP port 22, and Network Time Protocol (NTP), which operates over UDP port 123.
Secure Shell (SSH) provides secure, encrypted command-line sessions using TCP port 22. Network Time Protocol (NTP) synchronizes system clocks across network devices using connectionless UDP port 123.

Step-by-Step Solution

1
Determine the protocol and port required for secure remote command-line access.
SSH (Secure Shell) meets the requirement for encrypted terminal access and runs on TCP port 22.
Telnet operates on TCP port 23 but sends credentials and payload in unencrypted cleartext.
2
Determine the protocol, port, and transport layer for system clock synchronization.
NTP (Network Time Protocol) synchronizes device clocks using UDP port 123.
NTP requires low-overhead, latency-sensitive transport and is defined to run over connectionless UDP rather than TCP.

Key Concept

Port number and transport protocol mapping for SSH (TCP 22) and NTP (UDP 123).
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Topics

Common Ports and Protocols

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