What is the difference between 465 and 587?

465 is SMTP over implicit TLS; 587 is mail submission that upgrades with STARTTLS. Both are for clients sending mail; 25 is server-to-server.

Which ports should never be public?

Databases, Redis, Docker API 2375, SMB 445, RDP 3389 and similar management ports. Put them behind a VPN or allowlist.

Is this the full IANA registry?

No. It is a curated list of ports seen in real operations; the IANA registry has thousands of rarely used entries.

AppHelp

TCP/UDP port number lookup

Find what runs on a port, or which port a service uses. Each entry shows TCP/UDP, a short description and whether it should stay off the public internet.

Port number, range or service name

Try:

Results: 92Red tag: keep off the public internet

FTP-datatcpInsecure / legacy
FTP active-mode data channel
File sharing
FTPtcpInsecure / legacy
FTP control; credentials in clear text
File sharing
SSH / SFTPtcp
Secure shell, SFTP and SCP
Remote & VPN
TelnettcpInsecure / legacy
Unencrypted remote terminal
Remote & VPN
SMTPtcp
Mail transfer between servers
Email
DNStcpudp
Domain name resolution (UDP, TCP for large answers and zone transfers)
Network infra
DHCPudp
DHCP server (67) and client (68)
Network infra
TFTPudpInternal only
Trivial file transfer, PXE boot, switch configs
File sharing
HTTPtcp
Web traffic, ACME HTTP-01 challenges
Web
KerberostcpudpInternal only
Kerberos authentication (Active Directory)
Directory & auth
POP3tcpInsecure / legacy
Mail retrieval, unencrypted
Email
rpcbindtcpudpInternal only
ONC RPC portmapper (NFSv3)
File sharing
NNTPtcpInsecure / legacy
Usenet news
Messaging
NTPudp
Network time synchronisation
Network infra
MS-RPCtcpInternal only
Microsoft RPC endpoint mapper
Directory & auth
NetBIOStcpudpInternal only
NetBIOS name, datagram and session service
File sharing
IMAPtcp
Mail access, STARTTLS capable
Email
SNMPudpInternal only
SNMP polling of network devices
Monitoring
SNMP trapudpInternal only
SNMP traps sent by devices
Monitoring
BGPtcp
Border Gateway Protocol peering
Network infra
LDAPtcpudpInternal only
Directory access (Active Directory, OpenLDAP)
Directory & auth
HTTPS / QUICtcpudp
TLS web traffic; UDP 443 carries HTTP/3
Web
SMBtcpInternal only
Windows file sharing; never expose to the internet
File sharing
SMTPStcp
Mail submission over implicit TLS
Email
IKEudp
IPsec VPN key exchange
Remote & VPN
SyslogudpInternal only
Remote syslog
Monitoring
LPDtcpInternal only
Line printer daemon
File sharing
RIPudpInternal only
Routing Information Protocol
Network infra
DHCPv6udp
DHCPv6 client (546) and server (547)
Network infra
Submissiontcp
Mail submission with STARTTLS (clients send here)
Email
IPP / CUPStcpInternal only
Internet Printing Protocol
File sharing
LDAPStcpInternal only
LDAP over TLS
Directory & auth
DNS over TLS / QUICtcpudp
Encrypted DNS (DoT, DoQ)
Network infra
rsynctcpInternal only
rsync daemon
File sharing
FTPStcp
FTP over implicit TLS
File sharing
IMAPStcp
IMAP over TLS
Email
POP3Stcp
POP3 over TLS
Email
SOCKStcpInternal only
SOCKS proxy
Remote & VPN
OpenVPNudp
OpenVPN default
Remote & VPN
SQL ServertcpInternal only
Microsoft SQL Server
Databases
OracletcpInternal only
Oracle database listener
Databases
L2TPudp
L2TP VPN
Remote & VPN
PPTPtcpInsecure / legacy
PPTP VPN; broken crypto
Remote & VPN
RADIUSudpInternal only
RADIUS authentication (1812) and accounting (1813)
Directory & auth
MQTTtcpInternal only
MQTT broker, unencrypted
Messaging
SSDP / UPnPudpInternal only
UPnP discovery; abused for amplification
Network infra
NFStcpudpInternal only
Network File System
File sharing
ZooKeepertcpInternal only
ZooKeeper client port
Containers & cloud
Docker APItcpInternal only
Docker daemon without TLS; root access if exposed
Containers & cloud
Docker TLStcpInternal only
Docker daemon with TLS
Containers & cloud
etcdtcpInternal only
etcd client (2379) and peer (2380)
Containers & cloud
Dev server / GrafanatcpInternal only
Common dev server and Grafana default
Web
SquidtcpInternal only
Squid HTTP proxy
Web
AD Global CatalogtcpInternal only
Active Directory global catalog (3269 with TLS)
Directory & auth
MySQL / MariaDBtcpInternal only
MySQL and MariaDB
Databases
RDPtcpudpInternal only
Windows Remote Desktop; put behind a VPN
Remote & VPN
STUN / TURNtcpudp
NAT traversal for WebRTC
Voice & video
EPMDtcpInternal only
Erlang port mapper (RabbitMQ clusters)
Messaging
IPsec NAT-Tudp
IPsec NAT traversal
Remote & VPN
Docker Registry / FlasktcpInternal only
Docker registry, Flask and many dev servers
Containers & cloud
SIPtcpudp
VoIP signalling
Voice & video
SIPStcp
SIP over TLS
Voice & video
XMPPtcp
XMPP client connections
Messaging
mDNSudp
Multicast DNS / Bonjour
Network infra
PostgreSQLtcpInternal only
PostgreSQL
Databases
KibanatcpInternal only
Kibana UI
Monitoring
AMQPtcpInternal only
RabbitMQ AMQP
Messaging
VNCtcpInternal only
VNC remote desktop (5900 + display number)
Remote & VPN
WinRMtcpInternal only
Windows Remote Management HTTP (5985) / HTTPS (5986)
Remote & VPN
RedistcpInternal only
Redis; often unauthenticated
Databases
Kubernetes APItcpInternal only
Kubernetes API server
Containers & cloud
Syslog TLStcp
Syslog over TLS
Monitoring
BitTorrenttcpudp
BitTorrent peers
File sharing
HTTP alttcp
Alternate HTTP, proxies, Tomcat, Jenkins
Web
InfluxDBtcpInternal only
InfluxDB HTTP API
Monitoring
VaulttcpInternal only
HashiCorp Vault
Containers & cloud
HTTPS alttcp
Alternate HTTPS, admin panels
Web
ConsultcpInternal only
Consul HTTP API
Containers & cloud
MQTT TLStcp
MQTT over TLS
Messaging
MinIO / PHP-FPMtcpInternal only
MinIO S3 API, PHP-FPM, SonarQube
Containers & cloud
PrometheustcpInternal only
Prometheus server
Monitoring
KafkatcpInternal only
Apache Kafka broker
Messaging
node_exporter / JetDirecttcpInternal only
Prometheus node exporter; raw printing
Monitoring
ElasticsearchtcpInternal only
Elasticsearch / OpenSearch HTTP API
Databases
Elasticsearch transporttcpInternal only
Elasticsearch node-to-node transport
Databases
ZabbixtcpInternal only
Zabbix agent (10050) and server (10051)
Monitoring
KubelettcpInternal only
Kubelet API
Containers & cloud
MemcachedtcpudpInternal only
Memcached; UDP abused for amplification
Databases
Minecrafttcp
Minecraft Java server
Games
Steam / Sourcetcpudp
Source engine game servers
Games
MongoDBtcpInternal only
MongoDB
Databases
WireGuardudp
WireGuard default
Remote & VPN

Common tasks

port lookup
port number list
common ports
tcp udp ports
what port does
端口号查询

Quick answer

Type a port such as 3389 to see Windows Remote Desktop (TCP/UDP, keep behind a VPN), or type a service such as postgres to get 5432. Ranges like 8000-9000 list every known port inside.

How to use

1. SearchType a number, a range like 5000-6000 or a name like mysql.
2. FilterNarrow by category such as Databases or Email.
3. Read the notesRed tags mark services that should not face the internet.

Common use cases

Write firewall and security-group rules
Investigate an unknown open port from a scan
Remember mail ports 25, 465, 587, 993
Review which databases are exposed

Features

About 90 ports operators actually meet
Search by number, range or service name
TCP / UDP badges
Exposure and legacy-protocol warnings
Filter by category
Well-known / registered / ephemeral range explanation

Frequently asked questions

What is the difference between 465 and 587?: 465 is SMTP over implicit TLS; 587 is mail submission that upgrades with STARTTLS. Both are for clients sending mail; 25 is server-to-server.
Which ports should never be public?: Databases, Redis, Docker API 2375, SMB 445, RDP 3389 and similar management ports. Put them behind a VPN or allowlist.
Is this the full IANA registry?: No. It is a curated list of ports seen in real operations; the IANA registry has thousands of rarely used entries.