This topic lists some commonly used TCP port numbers and options that can be used when establishing connections.
| Port | Protocol | Comments |
|---|---|---|
| 7 | echo | |
| 11 | systat | |
| 15 | netstat | |
| 20 | ftp-data | |
| 21 | ftp | |
| 23 | telnet | |
| 25 | smtp | |
| 37 | time | |
| 43 | whois | |
| 53 | domain | DNS |
| 77 | rje | |
| 79 | Finger | |
| 80 | http | |
| 87 | link | ttylink |
| 95 | ||
| 101 | hostnames | |
| 109 | pop-2 | Post Office |
| 117 | uucp-path | |
| 119 | nntp | usenet – Network News Transfer |
| 123 | ntp | Network Time Protocol |
| 443 | https | Secure http |
| 465 | ssmtp | |
| 512 | exec | |
| 513 | login | |
| 514 | shell | cmd |
| 563 | snntp |
| Value | Meaning |
|---|---|
| SO_BROADCAST | Allow transmission of broadcast messages on the socket. |
| SO_DEBUG | Record debugging information. |
| SO_DONTLINGER | Don’t block close waiting for unsent data to be sent. |
| SO_DONTROUTE | Don’t route: send directly to interface. |
| SO_KEEPALIVE | Send keepalives. |
| SO_LINGER | Linger on close if unsent data is present. |
| SO_OOBINLINE | Receive out-of-band data in the normal data stream. |
| SO_RCVBUF | Specify buffer size for receives |
| SO_REUSEADDR | Allow the socket to be bound to an address that is already in use. |
| SO_SNDBUF | Specify buffer size for sends. |
| TCP_NODELAY | Disables the Nagle algorithm for send coalescing. |