6511

UDP port 6511 is the registered default listening port for DCCP-UDP, which carries Datagram Congestion Control Protocol (DCCP) packets inside UDP for NAT/NAPT traversal; whether it belongs on the public internet depends on an intended DCCP-UDP service and is otherwise Unknown. [IANA](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv) [RFC 6773](https://www.rfc-editor.org/rfc/rfc6773.txt)

RFC 6773 describes a UDP header inserted between IP and the DCCP packet. A server can listen on 6511 by default, or use a signaled port. Application-specific implementations are advised to use an ephemeral port and signal it out of band. The registration and protocol specification do not establish how often this is deployed or whether any particular host is listening.

The UDP checksum protects the encapsulated DCCP datagram and must be nonzero; receivers must drop packets with a zero or invalid checksum. The RFC also calls for validation of packet lengths before passing received payloads to DCCP. These protocol rules describe implementation behavior, not the security posture of a specific service.

Protocol

dccp-udp is the registered default UDP listener for DCCP-UDP encapsulation; deployment on any host is Unknown. [IANA](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv) [RFC 6773](https://www.rfc-editor.org/rfc/rfc6773.txt)

Exposure

Unknown; the specification supports NAT traversal but does not establish the intended audience or whether a particular host should be reachable publicly. [RFC 6773](https://www.rfc-editor.org/rfc/rfc6773.txt)

Protocol handling

UDP checksum must be nonzero and invalid or zero-checksum packets must be dropped. [RFC 6773](https://www.rfc-editor.org/rfc/rfc6773.txt)

Prevalence and malware

Unknown; supplied sources contain no scoped deployment measurement or malware observation.

IANA service

dccp-udp [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

IANA description

Datagram Congestion Control Protocol Encapsulation for NAT Traversal [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

RFC

RFC 6773 [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

Default listener

UDP 6511 is the default listening port for a DCCP-UDP server [Confirmed] — https://www.rfc-editor.org/rfc/rfc6773.txt

Host deployment and reachability

Unknown [Unknown] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv