Port 6121SPDY

Legacy SPDY multiplexes web requests over TCP; port 6121 is its IANA assignment, though modern deployments use HTTP/2.

transport: tcp
in transit: encrypted
assignment: official
risk: 1/10
lookups: 0

Technical Details

what runs on :6121

SPDY runs over TCP and was designed to operate over TLS. It multiplexes independent streams on a connection using framed control and data messages, with header compression, prioritization, and flow control. SPDY implementations commonly negotiated the protocol during TLS setup using NPN and were generally encountered on port 443; 6121 is the registered port, not a common modern deployment port. SPDY is obsolete and has been superseded by HTTP/2.

Security Information

exposure of :6121

risk score

1/ 10safe

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

web services averages 3.1 across 205 ports — this one sits 2.1 below.

in transit

encrypted

payloads are protected on the wire

assignment

official

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

reachable over

tcp

every listening transport is another surface to filter at the edge

security overview

A listener on this obscure port would warrant identifying the specific legacy SPDY implementation before allowing access. SPDY is obsolete, and its TLS protection does not make an unmaintained server safe; avoid exposing such a service to the internet and prefer current HTTP/2-capable software.

Record

iana registry entry

port: :6121
service: SPDY
transport: TCP
encryption: tls / encrypted
assignment: iana registered
risk: 1/10safe
category: Web Services
usage: SPDY is a deprecated web protocol designed to improve page loading by multiplexing requests over one connection. Port 6121 is assigned to it, but engineers are unlikely to find a current public listener here; SPDY was more commonly negotiated over TLS on port 443 and was superseded by HTTP/2.
lookups: 0rank 993
added: 2026-10-09
updated: 2026-10-09
references: IANA service name registry — port 6121

Something wrong?

This record is maintained by the engineers who use port 6121. 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 2026-10-09.

01edit any field on a page of its own
02a model checks it for accuracy and spam
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edit this record →back to the registry

Related Ports

all 205 in web services →

the 8 most looked-up other ports in web services — 205 ports carry that label.

port	service	proto	category	risk	views
:8888	Sun Answerbook & Alt HTTP	TCP	Web Services	caution	123.9k
:8000	Intel Remote Desktop / Alternate HTTP Port	TCP	Web Services	safe	84.3k
:8888	NewsEDGE	TCPUDP	Web Services	caution	83.3k
:8888	HTTP Alternative Port	TCP	Web Services	caution	76.5k
:8888	GNUmp3d Streaming HTTP	TCP	Web Services	caution	76.3k
:9080	Groove RPC	TCPUDP	Web Services	caution	70.8k
:8881	Atlasz Secure Server	TCP	Web Services	caution	67.6k
:80	HTTP	TCPUDP	Web Services	caution	67.3k

risk mix of the 8 listed

safe13%
caution88%

0 of 8 encrypted

Port :6121SPDY

Technical Details

Security Information

Related Ports

Port 6121SPDY