概要と適用範囲
IANA（RFC 6335）が管理するポート番号空間は、ウェルノウンポート（0〜1023）、登録済みポート（1024〜49151）、動的ポート（49152〜65535）に区分されています。
仕様一覧表＆マトリクス
キーワード、コード番号、またはディレクティブ名で即時検索
| キー / コード | 定義と詳細 | GEOセマンティック階層 | 仕様と補足 |
|---|---|---|---|
| 22 | Port 22 (SSH / SFTP) Secure Shell for encrypted remote command-line login and secure file transfers. ssh -p 22 user@server.example.com | ●Port 22 ↳TCP port ↳remote administration ↳SSH encrypted terminal | RFC 4251 Target for continuous internet brute-force attacks; best practice is to disable password login and enforce SSH keys. |
| 53 | Port 53 (DNS) Domain Name System resolution; queries primarily use UDP, while zone transfers use TCP. dig @8.8.8.8 -p 53 example.com | ●Port 53 ↳UDP/TCP port ↳core internet service ↳DNS name resolution | RFC 1035 Unencrypted; subject to ISP monitoring unless replaced with DoH (port 443) or DoT (port 853). |
| 80 | Port 80 (HTTP) HyperText Transfer Protocol for unencrypted web communication. http://example.com:80/ | ●Port 80 ↳TCP port ↳web server ↳unencrypted HTTP | RFC 9110 In modern infrastructure, Port 80 should immediately issue a 301 redirect to HTTPS port 443. |
| 443 | Port 443 (HTTPS / DoH / QUIC) HTTP over TLS/SSL; standard secure encrypted web communication channel. https://example.com:443/ | ●Port 443 ↳TCP/UDP port ↳encrypted web ↳HTTPS and HTTP/3 transport | RFC 8446 / RFC 9114 Uses TCP for HTTP/1.1 and HTTP/2; uses UDP (QUIC) for HTTP/3. |
| 25 | Port 25 (SMTP) Simple Mail Transfer Protocol for relaying email between mail transfer agents (MTAs). telnet mail.example.com 25 | ●Port 25 ↳TCP port ↳email infrastructure ↳server-to-server mail routing | RFC 5321 Blocked by residential ISPs and cloud providers (AWS, GCP) by default to prevent spam botnets. |
| 587 | Port 587 (SMTP Submission) Standard port for mail client-to-server submission with mandatory STARTTLS encryption. STARTTLS on Port 587 | ●Port 587 ↳TCP port ↳email submission ↳authenticated client mail submission | RFC 6409 Preferred port over legacy port 465 for desktop and web mail clients sending outbound messages. |
| 993 | Port 993 (IMAPS) Internet Message Access Protocol over TLS for secure retrieval and syncing of mailboxes. IMAP over SSL/TLS | ●Port 993 ↳TCP port ↳email sync ↳secure IMAP mailbox synchronization | RFC 8314 Replaced unencrypted Port 143 for syncing email folders across multiple devices. |
| 3306 | Port 3306 (MySQL / MariaDB) Default port for MySQL and MariaDB relational database server connections. mysql -h 127.0.0.1 -P 3306 -u root -p | ●Port 3306 ↳TCP port ↳database service ↳MySQL client wire protocol | IANA Registered Should never be exposed directly to the public internet; bind strictly to 127.0.0.1 or VPC private subnet. |
| 5432 | Port 5432 (PostgreSQL) Default port for PostgreSQL relational database server listener. psql -h localhost -p 5432 -U postgres | ●Port 5432 ↳TCP port ↳database service ↳PostgreSQL backend protocol | IANA Registered Configure pg_hba.conf to enforce scram-sha-256 and TLS connections. |
| 6379 | Port 6379 (Redis) Default port for Redis in-memory data store and caching service. redis-cli -h 127.0.0.1 -p 6379 | ●Port 6379 ↳TCP port ↳cache storage ↳Redis in-memory store protocol | IANA Registered Historically lacked authentication by default; never expose to public interfaces. |
Testing Port Connectivity with Netcat and Curl
# Test TCP handshake on port 443 with zero data transfer
nc -zv example.com 443
# Test if MySQL port 3306 is listening locally
netstat -tulpn | grep 3306
# Inspect TLS handshake on custom port 8443
curl -v https://example.com:8443/healthzNetcat (nc) and netstat allow verification of open listening sockets and firewall connectivity.
規格標準 FAQ
Why are ports 0 to 1023 called "privileged ports"?↓
関連技術エコシステムと次の学習ステップ
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関連技術解説記事
What Is the Domain Name System (DNS)?
Direct explanation of hierarchical domain resolution from root servers to zone files.
DNS vs DNS-over-HTTPS (DoH): Privacy & Security
Traditional UDP port 53 lookups compared to encrypted TLS-encapsulated DoH queries.
Troubleshooting: DNS Returns NXDOMAIN Error
Diagnose missing records, propagation lag, and nameserver delegation failures.
関連する技術Q&A
What Happens When a DNS TTL Expires?
Answer: When a DNS TTL expires, caching resolvers evict the record and must re-query the authoritative nameserver before responding to clients.
Can a CNAME Record Point to an IP Address?
Answer: No, RFC 1034 requires CNAME records to point exclusively to another domain name, never to raw IPv4 or IPv6 addresses.
Why Can't a CNAME Record Coexist With Other Records at the Zone Apex?
Answer: RFC 1034 requires that if a CNAME exists at a node, no other record data may exist there. Since a zone apex must have SOA and NS records, CNAME is prohibited.
実践ハンズオン診断ラボ
次のステップへ進む
DNS Resolution & Propagation Lab
Trace authoritative resolution from the root servers down to the zone file in the visual DNS workbench.