A network scenario using winpkfilter

Your logic, while different in implementation, resembles the way SOCKS5 handles UDP ASSOCIATE and generally looks okay. It follows a similar encapsulation approach: sending metadata to a proxy server, receiving a token, and prepending that token to future packets.

It does have similar limitations, particularly:

1. MTU constraints – As you noted, prepending a 32-byte token reduces the usable payload size, which can lead to issues with packets near the 1500-byte MTU threshold. This is a common limitation in encapsulation-based proxy schemes.

2. Race condition on registration – Instead of skipping and passing packets until the proxy replies with the token, consider queuing outgoing packets per destination and only releasing them once authorization is complete and the token is available. This would reduce packet loss and make the logic cleaner.

Overall, the approach is valid for certain scenarios, just be mindful of these trade-offs.

You’re not required to return the packet to the stack immediately — you can queue it and process it later if needed.

If you’re adding a custom header, keep in mind the extra overhead. However, instead of processing each UDP packet individually, consider implementing a session-like approach similar to TCP. For example, send an initial “initiate” packet to set up forwarding for all subsequent UDP packets from a specific IP and port to a designated destination. This reduces per-packet processing and handles large payloads more efficiently, since you don’t need to modify each UDP payload.