VZ FIOS and Intel TCP IPv6 Checksum Offload problems

Sean Donelan sean at donelan.com
Sat Aug 27 19:00:41 UTC 2022

Hopefully, my pain will help someone else.

I've had sporadic Internet slowdowns and stuck networking since IPv6 was 
enabled on my FIOS ONT a few months ago.

After too much troubleshooting, I found out some older Intel GbE ethernet 
cards have a IPv6 Checksum Offload incompatibility with certain fiber ONT 
terminals.  As Verizon is enabling IPv6 on its FIOS network, you might 
find intermittent network problems.

Intermittent are the worst kind of problems.

In some situations where a client machine is connected via some specific 
Optical Network Terminals (ONTs), and data is appended after the packet 
checksum, the network adapter can drop receive packets when using TCP-IPv6 
Checksum Offload for receive traffic.

Intel published an alert in 2017, but I didn't have IPv6 on FIOS then.


TLDR; turn off TCP IPv6 Checksum Offload

Affects all operating systems (Windows, BSD, Linux, etc) using the 
affected wired Intel ethernet controllers.  Not a problem with Intel 

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