Fix NS_E_MAX_PACKET_SIZE_TOO_SMALL (0XC00D0BD1) in 3 Steps

What's This Error?

You're getting NS_E_MAX_PACKET_SIZE_TOO_SMALL (0XC00D0BD1) when trying to stream video or audio over your local network. It means Windows can't handle the multicast packets coming through. I've seen this most often on Windows 10 and 11 machines after a VPN install or a security software update. One client had it after their IT guy locked down the firewall too tight.

The fix is usually straightforward. Start with the easiest thing, move up if it doesn't work. Don't waste time on stuff you don't need.

Step 1: Quick Registry Tweak (30 Seconds)

This is the most common fix. Windows has a hidden packet size limit for multicast streams that some software borks.

1. Press Win + R, type regedit, hit Enter.
2. Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters.
3. If you don't see a DWORD called MTU, right-click in the right pane, choose New > DWORD (32-bit), name it MTU.
4. Set its value to 1500 (decimal). That's the default Ethernet MTU.
5. Close regedit, restart your PC.

Had a client last month whose entire print queue died because of this — okay, not the print queue, but their streaming to a big screen went down. This fix got them back in 30 seconds.

If that didn't work, move on.

Step 2: Firewall Rule Adjustment (5 Minutes)

Windows Firewall or third-party firewalls often block multicast packets if they're too big. The fix is to allow them.

For Windows Firewall:

1. Open Control Panel > Windows Defender Firewall > Advanced Settings.
2. Click Inbound Rules > New Rule.
3. Choose Port, then UDP, and enter port 1900 (typical for UPnP multicast). Also try ports 5353 (mDNS) if you use Bonjour.
4. Allow the connection, apply to Domain, Private, and Public.
5. Name it something like "Allow Multicast UDP".

Also check for any rule that sets a packet size limit. Some security software like McAfee or Norton has a "Packet Size" filter — set it to "Default" or "Allow all".

I had a client whose corporate VPN was dropping packets over 1400 bytes. The fix was in the VPN client settings: look for "MTU size" and set it to 1500. If your VPN doesn't have that option, you might need to update it.

Still broken? Let's go deeper.

Step 3: Network Driver Tuning (15+ Minutes)

This is for when the registry and firewall didn't cut it. Sometimes the network driver's packet buffer or offloading settings are the culprit.

1. Open Device Manager (right-click Start button).
2. Expand Network adapters, find your active NIC (likely Realtek or Intel).
3. Right-click it > Properties > Advanced tab.
4. Look for these settings and change them:

Click OK, restart. If your NIC doesn't have these, don't sweat it — some drivers hide them.

Still no luck? Update your network driver from the manufacturer's site, not Windows Update. Realtek's site has newer drivers than what Windows gives you.

When Nothing Works

I've seen this error stick around in rare cases where the router itself is the problem. Some older routers (like Netgear WNR2000 from 2010) handle multicast packets poorly. If you've tried all three steps, try plugging directly into the router with a cable or test on a different network.

Also check if any software like TeamViewer, LogMeIn, or Citrix is running — they sometimes capture and resize network packets. Close them temporarily to test.

If you're still stuck after this, drop a comment with your setup — I've probably seen it before.