Port 3131Net Bookmark

Net Bookmark is an obscure service assigned to TCP and UDP port 3131.

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

Technical Details

what runs on :3131

Net Bookmark is registered on port :3131 over tcp and udp to Yiftach Ravid. 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 rarely. What's listening is often not the registered service, so check before you assume.

IANA has recorded this port being used for something it was not assigned for.

find what's listening on :3131

this machine

# linux
sudo ss -tulpn 'sport = :3131'

# macos / bsd
sudo lsof -nP -i :3131

# windows (then: tasklist /FI "PID eq <pid>")
netstat -ano | findstr :3131

another host

nmap -sV -p T:3131 <host>
sudo nmap -sU -sV -p U:3131 <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 :3131

risk score

1/ 10safe

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

network services averages 2.7 across 1,304 ports — this one sits 1.7 below.

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 :3131 yet

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

Record

iana registry entry

port: :3131
service: Net Bookmark
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 1/10safe
category: Network Services
usage: IANA assigns TCP and UDP port 3131 to the “Net Book Mark” service, registered to Yiftach Ravid. The assignment is rarely observed in Internet-wide scans, and IANA reports unauthorized use of the port.
lookups: 0rank 993
added: 2026-09-04
updated: 2026-09-04
references: IANA service name registry — port 3131

Something wrong?

This record is maintained by the engineers who use port 3131. 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 2026-09-04.

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

all 1,304 in network services →

the 8 most looked-up other ports in network services — 1,304 ports carry that label.

port	service	proto	category	risk	views
:9080	Groove RPC	TCPUDP	Web Services	caution	70.8k
:6543	Jetnet	UDP	Network Services	caution	65.3k
:5938	TeamViewer	TCPUDP	Remote Access	caution	65.0k
:8291	Winbox MikroTik Admin	TCP	Security	caution	62.9k
:3233	WhiskerControl Protocol	TCPUDP	Network Services	caution	61.9k
:3268	Microsoft Global Catalog (GC)	TCPUDP	Security	caution	54.6k
:135	Microsoft EPMAP	TCPUDP	Security	caution	51.9k
:3128	Tatsoft Default HTTP Proxy	TCP	Web Services	caution	46.8k

risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :3131Net Bookmark

Technical Details

Security Information

Related Ports

Port 3131Net Bookmark