Port 221Berkeley rlogind with SPX authentication

Berkeley rlogind remote-login service using SPX authentication on TCP and UDP port 221.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 7/10
lookups: 0

also known as fln-spx

Technical Details

what runs on :221

The registry assigns both TCP and UDP 221 to this service, although rlogind is fundamentally a session-oriented, byte-stream remote-login protocol and implementations would normally favor a connection-oriented transport. A Berkeley rlogin-style exchange typically begins with NUL-terminated local username, remote username, and terminal/speed fields, followed by bidirectional terminal data and control signaling; this variant adds SPX authentication. Standard Berkeley rlogin is commonly associated with TCP 513, so port 221 should be treated as a legacy or implementation-specific placement rather than the normal rlogin default.

Security Information

exposure of :221

risk score

7/ 10risk

treat as sensitive. widely scanned and regularly exploited when reachable — restrict it to known sources.

remote access averages 3.8 across 207 ports — this one sits 3.2 above.

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

rlogin-style services are generally unencrypted and historically rely on host-based trust such as .rhosts rather than strong user authentication. An exposed listener can disclose terminal traffic and permit unauthorized remote access if its trust configuration is weak; it should not be exposed directly to the Internet and should be replaced or isolated behind a secure management channel.

Record

iana registry entry

port: :221
service: Berkeley rlogind with SPX authentication
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 7/10risk
category: Remote Access System
usage: This port identifies a legacy Berkeley rlogind variant intended to provide remote terminal sessions with SPX authentication. It is unlikely on modern Internet hosts; an open port usually indicates legacy IPX/SPX-compatible software or a service-probe match.
lookups: 0rank 993
added: 2026-08-26
updated: 2026-09-22
references: IANA service name registry — port 221

Something wrong?

This record is maintained by the engineers who use port 221. 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 2026-09-22.

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Related Ports

all 207 in remote access →

the 8 most looked-up other ports in remote access — 207 ports carry that label.

port	service	proto	category	risk	views
:8000	Intel Remote Desktop / Alternate HTTP Port	TCP	Web Services	safe	84.3k
:8888	D2GS Admin Console	TCP	Remote Access	caution	83.7k
:8881	Atlasz Secure Server	TCP	Web Services	caution	67.6k
:5938	TeamViewer	TCPUDP	Remote Access	caution	65.0k
:8291	Winbox MikroTik Admin	TCP	Security	caution	62.9k
:8008	IBM HTTP Server Admin	TCP	Web Services	caution	58.3k
:135	Microsoft EPMAP	TCPUDP	Security	caution	51.9k
:23	Telnet	TCP	Remote Access	caution	34.8k

risk mix of the 8 listed

safe13%
caution88%

0 of 8 encrypted

Port :221Berkeley rlogind with SPX authentication

Technical Details

Security Information

Related Ports

Port 221Berkeley rlogind with SPX authentication