netdev - Re: [PATCH net-next] net: ipv4: Add ability to have GRE ignore DF bit in IPv4 payloads

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Message-Id: <20160610.230202.897629473050684544.davem@davemloft.net>
Date:	Fri, 10 Jun 2016 23:02:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	philipp@...fish-solutions.com
Cc:	netdev@...r.kernel.org, stephen@...workplumber.org
Subject: Re: [PATCH net-next] net: ipv4: Add ability to have GRE ignore DF
 bit in IPv4 payloads

From: "Philip Prindeville" <philipp@...fish-solutions.com>
Date: Tue,  7 Jun 2016 13:48:46 -0600

> From: Philip Prindeville <philipp@...fish-solutions.com>
> 
> In the presence of firewalls which improperly block ICMP Unreachable
> (including Fragmentation Required) messages, Path MTU Discovery is
> prevented from working.
> 
> A workaround is to handle IPv4 payloads opaquely, ignoring the DF bit--as
> is done for other payloads like AppleTalk--and doing transparent
> fragmentation and reassembly.
> 
> Reviewed-by: Stephen Hemminger <stephen@...workplumber.org>
> Signed-off-by: Philip Prindeville <philipp@...fish-solutions.com>

I think the feedback that this feature should be mutually exclusive
to pmtudisc is valid and you should address that.