Firewall or NAT boundary

RTSP works over TCP but UDP media is blocked

Sample RTSP Inspector report for a camera that negotiates UDP transport but delivers no RTP media to the client.

Download PDF sample Download RTSP Inspector All sample reports

HTML preview

What a customer handoff looks like

Failure boundary RTSP control and transport negotiation succeeded. UDP media did not arrive. TCP interleaved media is the working workaround.

Raw evidence excerpt

SETUP Transport: RTP/AVP;unicast;client_port=50000-50001; server accepted UDP; no matching RTP/RTCP received; TCP interleaved comparison produced media.

Summary

The camera accepted RTSP control and SETUP for UDP unicast, but no matching RTP packets reached the client. TCP interleaved playback worked, which moves the failure boundary to UDP routing, firewall, NAT, or port policy.

Failure boundary

RTSP control and transport negotiation succeeded. UDP media did not arrive. TCP interleaved media is the working workaround.

Likely cause

A firewall, NAT rule, VLAN boundary, VPN path, or host policy is blocking or misrouting UDP RTP/RTCP ports.

Confidence

High

Evidence screenshots

**UDP transport was accepted** The camera accepted the requested transport, moving the question from RTSP support to UDP delivery.

**RTP evidence separates media loss** The RTP stream view is where a field team records packet arrival, gaps, SSRC, timing, and missing media.

Evidence table

Layer	Finding	Implication
RTSP SETUP	The server accepted UDP unicast transport and returned server/client port negotiation.	The camera supports the requested mode; this is not a simple unsupported-transport error.
RTP receive	No RTP packets matching the negotiated stream arrived within the capture window.	The media plane is blocked after control-plane success.
RTCP	No usable RTCP sender report was observed for the negotiated UDP path.	The media timing channel is blocked or never reaches the client.
TCP comparison	The same camera produced media when RTSP interleaved TCP was used.	Credentials, stream path, and codec are unlikely to be the primary failure.

Recommended fix

Open the negotiated UDP RTP and RTCP port range between the camera/NVR subnet and the client.
If NAT or VPN is involved, prefer RTSP interleaved TCP unless symmetric UDP forwarding is controlled.
Record the exact client and server ports from SETUP in the firewall ticket.
Retest with the same RTSP URL using TCP interleaved mode as a temporary production workaround.