Re: [tcpm] draft-eggert-tcpm-historicize-00

Anantha,

I think for purposes of documenting "legacy" implementations, the
RFC1146 would still be valid.

I will try to define the goal of that recent proposal again, at least as
far as I understand this, so that we are all on the same page here.

Our expirience has shown, that TCP often runs over links with much
higher error rates, than intended for the technology (ie. Design goal of
BER <= 1E-12 over Ethernet often has an actual BER >> 1E-12). If such
error-prone links are running at a high speed and with large segment
sizes (jumbo / giant frames), there exists the real problem that within
a short timeframe (weeks to months), TCP will deliver corrupted data, as
CRC-16 was not able to catch the error.

>From my point of view, I understood the recent discussions around
RFC1146 in such a way, that for the intended purpose, which is to
provide a stronger payload checksum (equivalent to SCTP levels), a new
option would be required rather than reusing the alternate checksum
option. The reasoning is that currently deployed gear, especially NAT /
PAT gateways - which have to re-calculate the TCP Checksum as the
Pseudo-Header is changed - might know about the originally defined
alternate checksum algorithms, but not the new ones.

Furthermore, RFC1146 specifically requires the Pseudo Header to be
included - which one wouldn't want to do if only payload CRC is
required.

Providing a Payload-only CRC (ie. as the first TCP option), would enable
the transparent forwarding of such a new option by NAT/PAT gateways
without any problems.

Of course, if RFC1146 could be extended to include algorithms which
actually "violate" some of the specs of it, but maintain using the same
TCP options with a new algorithm codepoint, that would be fine with me.

But this would probably ask for a new RFC obsoliting RFC1146 anyway (in
effect making it again historic :) ).

Does that make sense?

Thanks for your comments!

Richard

> -----Original Message-----
> From: Anantha Ramaiah (ananth) [mailto:ananth@cisco.com] 
> Sent: Donnerstag, 24. Juni 2010 20:17
> To: Eddy, Wesley M. (GRC-MS00)[ASRC AEROSPACE CORP]; Lars 
> Eggert; tcpm@ietf.org
> Subject: Re: [tcpm] draft-eggert-tcpm-historicize-00
> 
> I have already communicated earlier that the TCP alternate 
> checksum option needs to be removed from this list. Reason 
> being it is still being used and there are proposals out 
> there that is trying to make use of this option. Other than 
> that point I am fine with this draft moving forward.
> 
> -Anantha
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