Port 2757Common Name Resolution Protocol

Port 2757 is assigned to CNRP, a niche protocol for resolving human-readable common names through directory services.

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

also known as cnrp

Technical Details

what runs on :2757

CNRP is a client/server query-and-response protocol: a client submits a common-name query to a CNRP service and receives matching results. IANA assigns port 2757 for both TCP and UDP. This is a distinct resolution protocol, not DNS; the port assignment itself does not provide encryption, and a listener on this port should be identified by its protocol exchange rather than assumed to be a standard resolver.

Security Information

exposure of :2757

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 1,331 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

CNRP is uncommon, so an unexpected listener on 2757 merits investigation. Queries and returned results should be treated as unencrypted unless protected by an external mechanism; restrict access to intended clients and avoid exposing a service that is not needed.

Record

iana registry entry

port: :2757
service: Common Name Resolution Protocol
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 1/10safe
category: Network Services
usage: CNRP is specified in RFC 3367 for querying common-name services and returning matching resolution results; it is not a general-purpose DNS listener. It is rarely encountered in ordinary networks, and IANA lists the assignment to Jacob Ulmert.
lookups: 0rank 993
added: 2026-09-24
updated: 2026-09-24
references: IANA service name registry — port 2757

Something wrong?

This record is maintained by the engineers who use port 2757. 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 2026-09-24.

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edit this record →back to the registry

Related Ports

all 1,331 in network services →

the 8 most looked-up other ports in network services — 1,331 ports carry that label.

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:3128	Tatsoft Default HTTP Proxy	TCP	Web Services	caution	46.8k

risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :2757Common Name Resolution Protocol

Technical Details

Security Information

Related Ports

Port 2757Common Name Resolution Protocol