UDP max recv bytes in single packet.

[prem111as]

Hi, Is there a way to increase the maximum size of a single packet from 1472 bytes to, for example, 2000 bytes? I have the option to re-compile MicroPython.

micropython ver v1.14

Regards.

[ctimmer]

Because UDP is a connection-less protocol the maximum packet size is usually limited to the minimum packet size the network can support. It is not a MicroPython limitation.

Curt

[prem111as]

This is very strange, I'm sending UDP packets from the same network to ESP up to 1472 bytes its ok packet received, anything above > 1472 bytes that the packet doesn't arrive at all. The same script in Python I run on Mac (in the same network) and I can receive 2000 bytes without problems.

[sosi-deadeye]

If I send more than 1472 bytes via UDP, it's sucked into a black hole. Nothing reaches the destination. I would not rely on more than 1472 bytes.

+ 20 byte IP header
+ 8 byte UDP header
+ 1472 payload
---------------------
1500 bytes

Btw. I find this answer helpful: https://stackoverflow.com/a/35697810/2817354

To be safe, do not use more than 508 bytes payload.

[prem111as]

Yes, I read that, thanks. I'm just wondering why when I receive data, for example on PC in a Python script, I can receive normally even over 2000 bytes at once.

[GitHubsSilverBullet]

Your PCs IP-Stack is able to handle fragmented packets and reassemble them before handing them over to the application. I'd try Wireshark and look for ICMP messages along those lines.

[prem111as]

Can we enable such fragmentation and reassembly in the micropython or esp-idf sources in lwip?

[GitHubsSilverBullet]

To put code in there just for those very rare border cases does not seem to be a sensible approach.
Keep in mind that quite a large amount of additional RAM would be needed as well.

Just splitting a big packet into two smaller ones is a solution achievable in just a few minutes.

[googlysmooth]

Stop

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On Mon, Sep 22, 2025, 11:25 AM prem111as ***@***.***> wrote: This is very strange, I'm sending UDP packets from the same network to ESP up to 1472 bytes its ok packet received, anything above > 1472 bytes that the packet doesn't arrive at all. The same script in Python I run on Mac (in the same network) and I can receive 2000 bytes individually without problems. — Reply to this email directly, view it on GitHub <#18121 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AE6JM4B5ZKR3QEFF565TXIL3UAIGZAVCNFSM6AAAAACHFRP5XKVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTINBXG44TKOA> . You are receiving this because you are subscribed to this thread.Message ID: <micropython/micropython/repo-discussions/18121/comments/14477958@ github.com>

[krismc]

I had an inbound packet size problem with an esp32 TCP connection via an LTE modem a while back ending up fixing it by increasing the uart Rx buffer size. Probably not relevant if you're using WiFi I guess.