Port 9901Endpoint Handlespace Redundancy Protocol (ENRP)

ENRP uses SCTP port 9901 for control traffic between servers managing a Reliable Server Pool handlespace.

transport: sctp
in transit: cleartext
assignment: official
risk: 2/10
lookups: 0

also known as enrp-sctp, ENRP, RSerPool ENRP, ENRP server channel

Technical Details

what runs on :9901

ENRP runs over SCTP on port 9901 and carries control messages between ENRP servers to maintain and exchange the handlespace: the mapping between service handles and registered pool elements. This is server-to-server control traffic, distinct from the ASAP protocol used by pool users and elements (commonly SCTP port 3863). The protocol is specified in RFC 5353; SCTP provides reliable message transport, but ENRP traffic is not encrypted by default.

Security Information

exposure of :9901

risk score

2/ 10safe

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

network services averages 2.6 across 1,862 ports — this one sits 0.6 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

sctp

every listening transport is another surface to filter at the edge

security overview

An exposed ENRP listener is an unusual control-plane service and should generally be reachable only by trusted RSerPool peers. Untrusted access could enable attempts to disrupt peer communication or interfere with handlespace data; restrict it with network ACLs and use available peer-authentication protections. SCTP does not encrypt the traffic by default.

Record

iana registry entry

port: :9901
service: Endpoint Handlespace Redundancy Protocol (ENRP)
transport: SCTP
encryption: cleartext
assignment: iana registered
risk: 2/10safe
category: Network Services
usage: This is the ENRP server channel in RSerPool, a framework for managing pools of redundant service endpoints. Engineers are most likely to encounter it between ENRP servers in a specialized clustered or high-availability deployment, not on ordinary internet-facing hosts.
lookups: 0rank 993
added: 2026-10-16
updated: 2026-10-16
references: IANA service name registry — port 9901
RFC 5353

Something wrong?

This record is maintained by the engineers who use port 9901. 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 2026-10-16.

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edit this record →back to the registry

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risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :9901Endpoint Handlespace Redundancy Protocol (ENRP)

Technical Details

Security Information

Related Ports

Port 9901Endpoint Handlespace Redundancy Protocol (ENRP)