VZ FIOS and Intel TCP IPv6 Checksum Offload problems

Sat Aug 27 22:36:39 UTC 2022

No. In fact, a lot of low-end Ethernet interfaces are completely implemented in interrupt-driven driver software that runs in the host OS (such as Windows). The only thing the hardware provides is the magnetically to transduce binary bit streams. 

Even MAC-address decode is in software, and as a result, broadcast storms can slow these hosts to a crawl as the CPU had to check and discard every broadcast packet as “not mine”. 

When these tasks are offloaded from the CPU to the Ethernet hardware, the CPU doesn’t need to perform these tasks, reducing CPU workload. These also offloading resources provide parallel computing and validation of checksums, which is otherwise computationally expensive. 

I don’t know how this particular ONT bug works, but I’m guessing that it results in checksum failures under certain conditions, leading to retransmissions. 

-mel via cell

> On Aug 27, 2022, at 3:08 PM, Michael Thomas <mike at mtcc.com> wrote:
> 
> 
>> On 8/27/22 12:00 PM, Sean Donelan wrote:
>> 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.
>> 
>> https://www.intel.com/content/www/us/en/download/19174/disabling-tcp-ipv6-checksum-offload-capability-with-intel-1-10-gbe-controllers.html 
>> 
>> 
>> 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 WiFi.
> 
> My reaction is "offload from what"? Isn't this all done in silicon?
> 
> Mike
> 