# Severe IPv6 TCP transfer issues on 13.0-RC1 and RC2



## blakehartshorn (Mar 14, 2021)

The short version, when I use FreeBSD 13, delivering data can take 5 minutes for 1MB over SSH or HTTP when using IPv6. This problem does not happen with IPv4. I installed FreeBSD 12 and Linux on that same device, neither had the problem.

Did some troubleshooting with Linode, have ultimately ruled the network itself out at this point. When the server is on FreeBSD 13, it can download quickly over IPv6, but not deliver. Started investigating after noticing my SSH session was lagging when cat'ing large files or running builds. This problem even occurs between VMs in the same datacenter. I generated a 1MB file of base64 garbage served by nginx for testing. IPv6 is being configured by SLAAC and on both 12 and 13 installs was setup by the installer. The adapter name is vtnet0, Linode uses Linux/KVM hosts for their virtual machines.

I tried searching but didn't spot anything here, my apologies if this is already on the radar. Does anyone know if config settings need to be different on 13? Did I maybe just find a real issue? I can provide any requested details. Thanks!


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## richardtoohey2 (Mar 14, 2021)

You might get more traction on a mailing list; I don't know which one would be best - maybe freebsd-stable?

There's been a few questions over 13.0 on there e.g. look at https://marc.info/?l=freebsd-stable&r=1&b=202103&w=2


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## blakehartshorn (Mar 15, 2021)

Sent a message over to freebsd-net. Thanks for the suggestion.


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## richardtoohey2 (Mar 21, 2021)

Looks like this _might_ have got fixed in RC3?  PR 254366


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