Port 33Display Support Protocol

Display Support Protocol is assigned to TCP and UDP port 33.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 1/10
lookups: 0

also known as dsp

Technical Details

what runs on :33

Display Support Protocol is registered on port :33 over tcp and udp to Ed Cain. We don't have a technical write-up for it beyond the IANA registry entry.

In nmap's internet-wide scan data this port is found open sometimes. What's listening is often not the registered service, so check before you assume.

find what's listening on :33

this machine

# linux
sudo ss -tulpn 'sport = :33'

# macos / bsd
sudo lsof -nP -i :33

# windows (then: tasklist /FI "PID eq <pid>")
netstat -ano | findstr :33

another host

nmap -sV -p T:33 <host>
sudo nmap -sU -sV -p U:33 <host>

run it? the handshake, the implementations you meet in the wild and the flags that matter come from the engineers who do.

add technical details

Security Information

exposure of :33

risk score

1/ 10safe

routine exposure. this port is rarely the way in on its own — keep it patched and logged and move on.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

no security notes recorded for :33 yet

known exploits, hardening advice, what a compromise looks like — suggest an edit if you know its exposure.

Record

iana registry entry

port: :33
service: Display Support Protocol
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 1/10safe
category: uncategorised
usage: The IANA assignment identifies TCP and UDP port 33 for Display Support Protocol. The assignment is registered to Ed Cain, but no further deployment or implementation details are recorded.
lookups: 0rank 993
added: 2026-08-21
updated: 2026-08-21
references: IANA service name registry — port 33

Something wrong?

This record is maintained by the engineers who use port 33. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-08-21.

01edit any field on a page of its own
02a model checks it for accuracy and spam
03clean and confident goes live immediately

edit this record →back to the registry

Related Ports

browse categories →

ports registered around :33, by lookups.

port	service	proto	category	risk	views
:80	HTTP	TCPUDP	Web Services	caution	67.3k
:23	Telnet	TCP	Remote Access	caution	34.8k
:83	MIT ML Device	TCP	Network Services	caution	23.1k
:81	Torpark Onion Routing	TCP	Web Services	caution	21.4k
:22	SSH	TCPUDPtls	Security	caution	20.3k
:42	NameServer (ARPA Hostname)	TCPUDP	Network Services	caution	17.2k
:53	DNS	TCPUDP	Network Services	safe	16.7k
:42	WINS	TCPUDP	Network Services	caution	16.4k

risk mix of the 8 listed

safe13%
caution88%

1 of 8 encrypted

Port :33Display Support Protocol

Technical Details

Security Information

Related Ports

Port 33Display Support Protocol