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uboot tftp transfer is not working on office/work laptop, but works on desktop, why?

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Problem Resolution

Office laptops usually will have VPN installed.
It appears that some VPN Clients will reconfigure MTU value to 1300 bytes, presumably as a requirement of the VPN tunnel or to minimize delays.

This means that when using a TFTP server with the option negotiation ON, when U-Boot requests a packet size of 1468 bytes, the server responds by fragmenting the packets. As U-Boot does not support IP fragmentation, the transfer does not work.

To overcome this MTU on the tftp server network interface must be 1500.

You can check the MTU on a Windows PC with:

netsh interface ipv4 show subinterfaces

And if configured to something different than 1500 bytes, you can change it with:

netsh interface ipv4 set subinterface n mtu=1500 store=persistent

Where 'n' is the interface numbers as listed by the show subinterfaces option above.





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