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Difficulty: HardCommon Ports and Protocols

A network security administrator is configuring egress filtering rules on a perimeter firewall for a multi-tenant application server. The server must authenticate external network access requests using centralized RADIUS authentication services and transmit secure transactional alert messages via encrypted email submission using STARTTLS. Which TWO of the following transport protocol and port combinations must be permitted outbound on the firewall to meet these operational requirements?

  1. UDP port 1812Answer
  2. TCP port 587Answer
  3. C
    TCP port 1812
  4. D
    TCP port 25

Answer

The firewall rules must permit UDP port 1812 for RADIUS authentication and TCP port 587 for secure SMTP submission via STARTTLS.
The requirement for centralized RADIUS authentication requires opening UDP port 1812 outbound, as RADIUS uses UDP for authentication datagrams. The requirement for encrypted email submission via STARTTLS requires opening TCP port 587, which is the standardized port for client-to-server mail submission with TLS encryption.

Step-by-Step Solution

1
Identify the standard protocol and transport layer requirements for RADIUS AAA authentication.
RADIUS authentication uses UDP as its transport protocol on standard port 1812 (with accounting on UDP port 1813).
RADIUS relies on connectionless UDP transport for low-overhead authentication datagram exchange.
2
Identify the standard protocol and transport layer requirements for secure email submission.
Encrypted client-to-server mail submission using STARTTLS standardizes on TCP port 587.
TCP port 587 is designated for mail user agents submitting mail to a mail transfer agent with opportunistic TLS security.
3
Evaluate the incorrect options against protocol specifications.
TCP port 1812 misidentifies RADIUS as connection-oriented TCP, while TCP port 25 refers to unencrypted legacy server-to-server SMTP relay.
Matching transport protocol types (TCP vs UDP) and specific service ports is required for precise firewall ACL definition.

Key Concept

Standard default port numbers and transport layer protocols for RADIUS authentication and secure SMTP mail submission
Estimated Time:2m 0s
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Topics

Common Ports and Protocols

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