netdev - Re: [net PATCH 2/2] ipv4/GRO: Make GRO conform to RFC 6864

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Date:	Fri, 01 Apr 2016 19:21:49 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	alexander.duyck@...il.com, aduyck@...antis.com,
	herbert@...dor.apana.org.au, tom@...bertland.com, jesse@...nel.org,
	edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [net PATCH 2/2] ipv4/GRO: Make GRO conform to RFC 6864

On Fri, 2016-04-01 at 22:16 -0400, David Miller wrote:
> From: Alexander Duyck <alexander.duyck@...il.com>
> Date: Fri, 1 Apr 2016 12:58:41 -0700
> 
> > RFC 6864 is pretty explicit about this, IPv4 ID used only for
> > fragmentation.  https://tools.ietf.org/html/rfc6864#section-4.1
> > 
> > The goal with this change is to try and keep most of the existing
> > behavior in tact without violating this rule?  I would think the
> > sequence number should give you the ability to infer a drop in the
> > case of TCP.  In the case of UDP tunnels we are now getting a bit more
> > data since we were ignoring the outer IP header ID before.
> 
> When retransmits happen, the sequence numbers are the same.  But you
> can then use the IP ID to see exactly what happened.  You can even
> tell if multiple retransmits got reordered.
> 
> Eric's use case is extremely useful, and flat out eliminates ambiguity
> when analyzing TCP traces.

Yes, our team (including Van Jacobson ;) ) would be sad to not have
sequential IP ID (but then we don't have them for IPv6 ;) )

Since the cost of generating them is pretty small (inet->inet_id
counter), we probably should keep them in linux. Their usage will phase
out as IPv6 wins the Internet war...