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ProtocolPorts

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Well-known, registered, and dynamic ports explained
Understand the IANA port ranges: well-known (0-1023), registered (1024-49151), and dynamic (49152-65535), plus how the 16-bit port space and ephemeral ports work.
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What ports does Active Directory use?
The full list of ports a domain controller needs — Kerberos, LDAP, SMB, RPC, Global Catalog — plus why none of them should ever face the internet.
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What ports does DNS use? 53, DoT, mDNS & LLMNR
DNS uses port 53 over both UDP and TCP, with DNS-over-TLS on 853, mDNS on 5353 and LLMNR on 5355. Learn why, plus DNS attacks and how to encrypt lookups.
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What ports does email use? SMTP, IMAP & POP3
A complete guide to email ports: SMTP 25, submission 587, SMTPS 465, POP3 110/995, IMAP 143/993 — when to use each and how to secure them with TLS.
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What ports does FTP use? FTP, FTPS and SFTP ports explained
FTP uses port 21 for control and port 20 for data, with FTPS on 990. Learn active vs passive mode, why SFTP is really SSH on port 22, and what to use.
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What ports does SMB use?
SMB and CIFS use port 445 today, with legacy NetBIOS on 137 and 139. Here is what each does, why 445 is the top ransomware vector, and what to block.
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