Author Topic: Dissapearing packets over certain 4G networks  (Read 262 times)

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Offline deadly_penguin

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Dissapearing packets over certain 4G networks
« on: October 16, 2020, 09:27:20 am »
Hi,
I have two embedded devices trying to talk over a 4G gateway. One can successfully open a connection to the server, the other (using an old Microchip tcp/ip stack) can send a SYN, get a response, ACK it and send the HTTP request, but the HTTP request won't reach the server. Apart from window size and scaling (the one that won't work has a much smaller window size and no scaling), and a few options, the packets are almost identical.

It's also network dependant - everything is fine on EE, but breaks on O2.

Anyone have any suggestions?
 

Offline Halcyon

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Re: Dissapearing packets over certain 4G networks
« Reply #1 on: October 26, 2020, 03:53:27 am »
Without knowing exactly what the set up, is it possible that carrier grade NAT is breaking things? It's common on cellular networks (and even many fixed wire networks) not to have a public IPv4 address.
 
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Offline deadly_penguin

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Re: Dissapearing packets over certain 4G networks
« Reply #2 on: October 27, 2020, 01:38:15 pm »
Thanks,
We fixed it eventually. It turned out that on certain carriers that use a transparent proxy, the proxy was getting upset by the Window Size that the Microchip stack was setting and just black-holing the packets. 
 
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