Cannot connect to NTRIP caster

NTRIP connection failures have a small number of root causes. Work through this guide from the top — most problems are solved within the first three checks.

Quick diagnostic checklist

Before diving into causes, run through these five checks. They resolve the majority of NTRIP connection failures.

Quick NTRIP diagnostic

Internet working? Open a browser and load any website. If it fails, fix your connection first.
Correct host and port? Port must be 2101. Host must match exactly — no typos and no http:// prefix.
Credentials correct? Username and password are case-sensitive. Copy-paste rather than typing.
Mountpoint exists? Load the sourcetable from the server to confirm the mountpoint name.
GGA enabled? Required for VRS mountpoints. It must be enabled in your NTRIP client.

Cause 1 — No internet connection

Device has no data connection

Most common cause on first setup

NTRIP corrections travel over a standard internet connection. If your device cannot reach the internet, it cannot reach the NTRIP server — regardless of how correctly everything else is configured.

Open a browser on the same device and navigate to any website. If it does not load, resolve the connectivity issue before proceeding.
If you use a receiver with a built-in SIM card (Emlid RS3, RS4 or some Trimble units), verify the SIM has an active data plan and signal bars are showing.
If you use a phone hotspot, check that the device connecting to the hotspot actually has internet access through it — not just a Wi-Fi connection to the hotspot.
In areas with weak cellular signal, switch between 4G and 3G modes. A stable 3G connection is better than an unstable 4G one for NTRIP streaming.

Cause 2 — Port 2101 is blocked

Firewall or carrier blocking TCP port 2101

Common on corporate networks and some mobile carriers

NTRIP uses TCP port 2101. Some corporate Wi-Fi networks and mobile carriers block outbound connections on non-standard ports. If you have general internet access but cannot reach the NTRIP server, port blocking is likely.

Switch networks. If you are on corporate Wi-Fi, switch to mobile data. If you are on mobile data, try a different carrier's SIM or a Wi-Fi network at home.
Use a personal hotspot. Create a hotspot from your phone's mobile data connection and connect your field device to it. This bypasses most corporate network restrictions.
Ask IT to open the port. On a corporate network, request that TCP port 2101 outbound is opened for your device. This is a standard NTRIP requirement.
Test the port directly. On a computer, open a terminal and run telnet ntrip.rtksub.com 2101. If the connection opens, the port is accessible. If it times out, the port is blocked.

Quick port test on Android

Install the free app Port Authority on Android. Enter the NTRIP host and port 2101, then tap Scan. A green result means the port is reachable. A red result means it is blocked on your current network.

Cause 3 — Wrong credentials or mountpoint

Authentication failure or unknown mountpoint

Connection reaches the server but is rejected

If the server is reachable but your client receives an error like 401 Unauthorized or 404 Not Found, the problem is the credentials or mountpoint name.

Check for typos. Username and password are case-sensitive. Copy and paste from your service confirmation email rather than typing manually.
Load the sourcetable. Most NTRIP clients have a Get Mountpoints or Source Table button. Use it to fetch the current list of available mountpoints from the server — do not type the mountpoint name manually.
Check your subscription status. If your trial or subscription has expired, the server will reject your credentials even though they look correct.
Verify the host address. Do not include http:// or https:// before the hostname. Enter the hostname only — for example ntrip.rtksub.com — and set the port separately to 2101.

Hostntrip.rtksub.com

Port2101

Mountpoint — standardRTCM3_NL

Mountpoint — DJI dronesRTCM3_NL_MSM5

Mountpoint — VRS (>30 km)RTCM3_NL_VRS

Mountpoint — high-endRTCM3_NL_MSM7

Cause 4 — GGA not being sent

No GGA position being transmitted to server

Affects VRS mountpoints — connection appears successful but no data flows

VRS (Virtual Reference Station) mountpoints require your rover to send its approximate position to the NTRIP server. The server uses this to generate a virtual correction point near you. If GGA is not sent, the server streams nothing — you are connected but receive 0 bytes per second.

In your NTRIP client settings, look for Send GGA to caster, Transmit NMEA GGA or Send position to server. Enable it.
Make sure your receiver has at least a Single solution before connecting. GGA requires a valid position — even a rough one. If GGA contains all zeros, the server cannot generate corrections.
If you are not using VRS but still see 0 bytes, try switching to a non-VRS mountpoint such as RTCM3_NL. Standard mountpoints do not require GGA.

Device-specific fixes

Select your device for tailored instructions:

Emlid Flow (Reach RS2+, RS3, RS4, RX2): Go to Correction input → NTRIP. Tap Add profile and fill in the credentials. Enable Send GGA to caster if you use a VRS mountpoint. Make sure the receiver has satellite lock (Single or better) before connecting.

If the connection fails with correct credentials, toggle airplane mode on and off to refresh the data connection, then reconnect.

For Emlid on Windows with FieldGenius: configure NTRIP inside Emlid Flow via the receiver's IP, not inside FieldGenius.

In DJI Pilot 2, go to RTK Settings → Custom Network RTK and check the host, port and credentials. Use RTCM3_NL_MSM5 for DJI drones, or RTCM3_NL_VRS for long baselines. Make sure the controller has internet access before connecting.

Open NTRIP Client only after connecting the external receiver. The option does not appear without an active Bluetooth GNSS or USB Serial GNSS connection. Enable Send NMEA GGA to NTRIP Caster for VRS.

Confirm the controller has an active internet data link, then reload the sourcetable rather than entering a mountpoint manually. In Trimble Access, check the received-byte counter under the receiver's Data Link status.

In Lefebure NTRIP Client, add a new profile and use the Get Source Table button. Allow the app to use mobile data, and enable GGA when the selected mountpoint is VRS.

Common error messages

Error message	Meaning	Fix
`401 Unauthorized`	Wrong username or password	Check credentials. Copy-paste from your account dashboard.
`404 Not Found`	Mountpoint does not exist	Load the sourcetable and select a mountpoint from the list.
`Connection refused`	Port 2101 blocked or server unreachable	Switch to mobile data. Test the port with telnet or Port Authority.
`Connection timeout`	No route to server — network or firewall issue	Check the internet connection. Try a different network.
Connected, 0 bytes/sec	GGA not sent for VRS, or wrong mountpoint	Enable GGA. Switch to a non-VRS mountpoint as a test.
`ICY 200 OK` then drops	Successful connection but stream interrupted	Unstable internet. Use a hotspot and enable auto-reconnect.
`Sourcetable empty`	Server reachable but no mountpoints returned	Your subscription may be inactive. Contact your correction service.

Still stuck?

If none of the above resolves the issue, the problem may be specific to your receiver model or network environment. Describe your exact error message, device and current network setup to the AI for a targeted answer.

Cannot connect to NTRIP caster — what now?

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