Re: why not enable tcp_pmtud_blackhole_detect in default

[Cui, Cheng]

Kevin,

Thanks for the reply. I think you have answered most of my doubts. But I would 
like to be clear that, is there a very strong reason why you run this in 
production even it often causes unnecessary lower MSS with lower performance?

Thanks,
Cheng Cui

On 3/7/18, 3:35 PM, "Kevin Bowling"  wrote:

Cheng,

We run this in production at Limelight Networks (i.e toward a broad
spectrum of Internet hosts) and must to deal with some uncommon
network topology. There are currently some limitations as you point
out.

Like you say the signaling is not perfect and we do often clamp MSS
unnecessarily.  There is also no probing to see if we can expand the
MSS later.

I think those issues should be fixed up before it's enabled by default
and I don't know anyone working on it at the moment.

Regards,

On Wed, Mar 7, 2018 at 8:35 AM, Cui, Cheng  wrote:
> Dear all,
>
> Reading through the tcp blackhole detection code (support RFC 4821) in 
FreeBSD including the recent bug fixes, I am wondering why is it still not 
enabled in default? Given the fact that this implementation was a merge from 
xnu, and the xnu has enabled it in default, do we have a plan to enable it in 
default? Or is there any concern about the side-effect from it as performance 
regression against some false positive blackhole event like a temporary link 
flap, which is long enough to trigger a lower MSS but shorter than 6 RTO?
>
> 
https://opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/netinet/tcp_timer.c.auto.html
  << enabled in macOS 10.6
> https://reviews.freebsd.org/rS322967  << bug fixes
> https://reviews.freebsd.org/rS272720  << merge from xnu
>
> Thanks,
> --Cheng Cui
> NetApp Scale Out Networking
> https://netapp-meeting.webex.com/meet/chengc
>
>
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> freebsd-net@freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/freebsd-net
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Re: why not enable tcp_pmtud_blackhole_detect in default

[Kevin Bowling]

Cheng,

We run this in production at Limelight Networks (i.e toward a broad
spectrum of Internet hosts) and must to deal with some uncommon
network topology. There are currently some limitations as you point
out.

Like you say the signaling is not perfect and we do often clamp MSS
unnecessarily.  There is also no probing to see if we can expand the
MSS later.

I think those issues should be fixed up before it's enabled by default
and I don't know anyone working on it at the moment.

Regards,

On Wed, Mar 7, 2018 at 8:35 AM, Cui, Cheng  wrote:
> Dear all,
>
> Reading through the tcp blackhole detection code (support RFC 4821) in 
> FreeBSD including the recent bug fixes, I am wondering why is it still not 
> enabled in default? Given the fact that this implementation was a merge from 
> xnu, and the xnu has enabled it in default, do we have a plan to enable it in 
> default? Or is there any concern about the side-effect from it as performance 
> regression against some false positive blackhole event like a temporary link 
> flap, which is long enough to trigger a lower MSS but shorter than 6 RTO?
>
> https://opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/netinet/tcp_timer.c.auto.html
>   << enabled in macOS 10.6
> https://reviews.freebsd.org/rS322967  << bug fixes
> https://reviews.freebsd.org/rS272720  << merge from xnu
>
> Thanks,
> --Cheng Cui
> NetApp Scale Out Networking
> https://netapp-meeting.webex.com/meet/chengc
>
>
> ___
> freebsd-net@freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/freebsd-net
> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
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why not enable tcp_pmtud_blackhole_detect in default

[Cui, Cheng]

Dear all,

Reading through the tcp blackhole detection code (support RFC 4821) in FreeBSD 
including the recent bug fixes, I am wondering why is it still not enabled in 
default? Given the fact that this implementation was a merge from xnu, and the 
xnu has enabled it in default, do we have a plan to enable it in default? Or is 
there any concern about the side-effect from it as performance regression 
against some false positive blackhole event like a temporary link flap, which 
is long enough to trigger a lower MSS but shorter than 6 RTO?

https://opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/netinet/tcp_timer.c.auto.html
  << enabled in macOS 10.6
https://reviews.freebsd.org/rS322967  << bug fixes
https://reviews.freebsd.org/rS272720  << merge from xnu

Thanks,
--Cheng Cui
NetApp Scale Out Networking
https://netapp-meeting.webex.com/meet/chengc


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