Port 4556Bundle Protocol TCP Convergence-Layer Protocol (TCPCL)

TCPCL carries Delay-Tolerant Networking bundles between DTN nodes over TCP.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 2/10
lookups: 0

also known as dtn-bundle, TCPCL, DTN Bundle TCP CL Protocol

Technical Details

what runs on :4556

TCPCL is the Bundle Protocol convergence layer defined in RFC 9174 (version 4; RFC 7242 describes version 3). A node opens a TCP connection, exchanges a contact header and session parameters, then transfers bundles in framed segments over TCP's reliable, ordered byte stream. The standard TCP port is 4556. IANA also lists UDP for this assignment, but that does not make TCPCL a UDP protocol; a UDP listener would need to be identified separately.

Security Information

exposure of :4556

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 1,551 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

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

TCPCL does not encrypt traffic by default, so bundle contents and session metadata can be exposed to a network observer unless the deployment adds protection such as TLS or uses security mechanisms at the Bundle Protocol layer. An exposed listener may accept unwanted peers or be used to consume resources or deliver unauthorized bundles if peer access is not restricted. This is a niche service and has not been observed open in the cited internet-wide scan data; it generally belongs on a controlled DTN network, not exposed indiscriminately.

Record

iana registry entry

port: :4556
service: Bundle Protocol TCP Convergence-Layer Protocol (TCPCL)
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 2/10safe
category: Network Services
usage: DTN routers and other bundle nodes use TCPCL to exchange bundles across intermittently connected or otherwise challenged networks. It is a specialized protocol rather than a common public-internet service; IANA lists the assignment for TCP and UDP, though TCPCL itself is TCP-based.
lookups: 0rank 993
added: 2026-10-05
updated: 2026-10-05
references: IANA service name registry — port 4556
RFC 7122
RFC 9174

Something wrong?

This record is maintained by the engineers who use port 4556. 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 2026-10-05.

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Related Ports

all 1,551 in network services →

the 8 most looked-up other ports in network services — 1,551 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 :4556Bundle Protocol TCP Convergence-Layer Protocol (TCPCL)

Technical Details

Security Information

Related Ports

Port 4556Bundle Protocol TCP Convergence-Layer Protocol (TCPCL)