3503

IANA assigns TCP port 3503 the service name lsp-ping, described as “MPLS LSP-echo Port,” and references RFC 8029. The registration identifies the port’s intended association; it does not establish that a host runs a service there or that it should be publicly reachable. The evidence does not establish the intended audience for TCP on this port, so an access policy cannot be determined from it alone.

RFC 8029 defines MPLS echo request and reply messages to detect data-plane failures in MPLS Label Switched Paths and help localize faults. It distinguishes ping mode, which checks end-to-end connectivity, from traceroute mode, which probes transit routers to isolate faults and compare forwarding with the control plane.

The RFC specifies these messages as UDP packets, potentially MPLS-labeled. That protocol description does not establish TCP behavior for port 3503. Treat the IANA TCP assignment as a registry fact, not evidence of observed deployment or traffic.

Assignment

IANA registers lsp-ping for TCP 3503 as “MPLS LSP-echo Port,” referencing RFC 8029.

Protocol context

RFC 8029 describes MPLS LSP echo diagnostics over UDP; it does not establish TCP operation.

Exposure

Unknown. The evidence does not establish the intended audience or whether TCP 3503 should be reachable from the public internet.

IANA service

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

IANA description

MPLS LSP-echo Port [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

IANA RFC reference

RFC 8029 [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

MPLS echo purpose

Detect data-plane failures in MPLS Label Switched Paths [Confirmed] — https://www.rfc-editor.org/rfc/rfc8029.txt

RFC transport description

MPLS echo request/reply messages use UDP [Confirmed] — https://www.rfc-editor.org/rfc/rfc8029.txt

TCP deployment and public reachability

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