Comcast - Significant v4 vs v6 throughput differences, almost stateful.

Dovid Bender dovid at telecurve.com
Thu Apr 23 15:24:42 UTC 2020


We have customers in CT with the same issues. When did this start?


On Thu, Apr 23, 2020 at 11:07 AM Nick Zurku <nzurku at teraswitch.com> wrote:

> Hello all,
>
> I would appreciate if someone from Comcast could contact me about this.
>
> We’re having serious throughput issues with our AS20326 pushing packets to
> Comcast over v4. Our transfers are either the full line-speed of the
> Comcast customer modem, or they’re seemingly capped at 200-300KB/s. This
> behavior appears to be almost stateful, as if the speed is decided when the
> connection starts. As long as it starts fast it will remain fast for the
> length of the transfer and slow if it starts slow. Traces seem reasonable
> and currently we’ve influenced the path onto GTT both ways. If we prepend
> and reroute on our side, the same exact issue with happen on another
> transit provider.
>
> This issue does not affect v6 and that is full speed on every attempt.
> This may be regionalized to the Comcast Pittsburgh market.
>
> This is most widely affecting our linux mirror repository server:
> http://mirror.pit.teraswitch.com/
> Our colocation customers who are hosting VPN systems are also noticing
> bottlenecks have started recently for their Comcast employees.
>
> --
> Nick Zurku
> Systems Engineer
> TeraSwitch, Inc.
> nzurku at teraswitch.com
>
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