Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

•  20/21 – File Transfer Protocol (FTP)
•  22 – Secure Shell (SSH)
•  23 – Telnet
•  25 – Simple Mail Transfer Protocol (SMTP)
•  53 – Domain Name System (DNS)
•  67/68 – Dynamic Host Configuration Protocol (DHCP)
•  80 – Hypertext Transfer Protocol (HTTP)
•  110 – Post Office Protocol 3 (POP3)
•  137/139 – Network Basic Input/Output System (NetBIOS)/NetBIOS over TCP/IP (NetBT)
•  143 – Internet Mail Access Protocol (IMAP)
•  161/162 – Simple Network Management Protocol (SNMP)
•  389 – Lightweight Directory Access Protocol (LDAP)
•  443 – Hypertext Transfer Protocol Secure (HTTPS)
•  445 – Server Message Block (SMB)/Common Internet File System (CIFS)
•  3389 – Remote Desktop Protocol (RDP)

TCP vs. UDP

•  Connectionless
•  DHCP
•  Trivial File Transfer Protocol (TFTP)
•  Connection-oriented
•  HTTPS
•  SSH

Always consider corporate policies, procedures and impacts before implementing changes

• Identify the problem

• Gather information from the user, identify user changes, and, if applicable, perform backups before making changes

• Inquire regarding environmental or infrastructure changes

Establish a theory of probable cause

• If necessary, conduct external or internal research based on symptoms

Test the theory to determine the cause

• Once the theory is confirmed, determine the next steps to resolve the problem

• If the theory is not confirmed, re-establish a new theory or escalate

Establish a plan of action to resolve the problem and implement the solution

• Refer to the vendor's instructions for guidance

Verify full system functionality and, if applicable, implement preventive measures Document the findings, actions,and outcomes