netdev - Re: [PATCH] ipv6: Limit mtu to 65572 bytes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 10 Apr 2014 20:14:50 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	David Miller <davem@...emloft.net>,
	Francois WELLENREITER <f.wellenreiter@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: Limit mtu to 65572 bytes

On Fri, 2014-04-11 at 04:57 +0200, Hannes Frederic Sowa wrote:
> On Fri, Apr 11, 2014 at 11:30:44AM +0900, YOSHIFUJI Hideaki wrote:
> > Eric Dumazet wrote:
> > 
> > > We must limit the IPv6 MTU to (65535 + 40) bytes in theory.
> > > 
> > > In practice, its better to align to a multiple of 4 for optimal TCP
> > > performance.
> > 
> > It is a TCP issue.  We should not limit the mtu to 65532+40.
> > I am for 65535+40. Otherwise, other protocol such as UDP cannot
> > use full mtu as before.
> 
> I have not seen problems with max ipv6 mtu limit of 65535+40 and tcp.
> 
> I agree this would be a better approach, and maybe & ~3 the mtu/mss
> in tcp code? I assume people expect maximum udp packet sizes working
> over loopback?

Yes, recent Intel cpus have really fast mem copy, even with different
alignments for source/dest.

But old cpus or other arches might have an issue here. Apparently nobody
really cares, so I wont argue and send a V2.




--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html