netdev - Re: [Bugme-new] [Bug 8756] New: Route advmss copied to ALL routes when interface MTU changes

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Message-ID: <4699D5C7.2090906@simon.arlott.org.uk>
Date:	Sun, 15 Jul 2007 09:07:35 +0100
From:	Simon Arlott <simon@...e.lp0.eu>
To:	netdev@...r.kernel.org
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"bugme-daemon@...nel-bugs.osdl.org" 
	<bugme-daemon@...nel-bugs.osdl.org>
Subject: Re: [Bugme-new] [Bug 8756] New: Route advmss copied to ALL routes
 when interface MTU changes

On 15/07/07 05:48, Andrew Morton wrote:
> On Sat, 14 Jul 2007 15:34:31 -0700 (PDT) bugme-daemon@...zilla.kernel.org wrote:
> 
>> http://bugzilla.kernel.org/show_bug.cgi?id=8756
> 
> It is unclear which kernel version this applies to?

Linus' 2.6 tree, as of Mon Jul 9 15:50:56 2007 -0700

For some reason it says "Version: 2.5" on the email and "Version: " on
the website...

> 
>>            Summary: Route advmss copied to ALL routes when interface MTU
>>                     changes
>>            Product: Networking
>>            Version: 2.5
>>           Platform: All
>>         OS/Version: Linux
>>               Tree: Mainline
>>             Status: NEW
>>           Severity: normal
>>           Priority: P1
>>          Component: IPV6
>>         AssignedTo: yoshfuji@...ux-ipv6.org
>>         ReportedBy: bugzilla@...e.lp0.eu
>> 
>> 
>> Steps to reproduce:
>> 1. Have multiple network devices and routes for them with standard (low, i.e.
>> 1500) MTUs and default ADVMSS (e.g. 1440)
>> 2. Change the MTU on one of them to something high (e.g. 7200)
>> 3. The ADVMSS is incorrectly set for ALL routes based on the new MTU of the
>> interface that changed.
>> 
>> Note: if addrconf is running then the ADVMSS will be reset on the next RA, so
>> this will impede attempts to reproduce.
>> 
>> # ip -6 r
>> fe80::/64 dev sit0  metric 256  expires 4481744sec mtu 1480 advmss 1440
>> hoplimit 4294967295
>> fe80::/64 dev ppp0  metric 256  expires 19071345sec mtu 1500 advmss 1440
>> hoplimit 4294967295
>> fe80::/64 dev eth0  metric 256  expires 19072430sec mtu 1500 advmss 1440
>> hoplimit 4294967295
>> default dev ppp0  metric 1024  expires 19071347sec mtu 1500 advmss 1440
>> hoplimit 4294967295
>> 
>> # ifconfig eth0 mtu 7200
>> 
>> # ip -6 r
>> fe80::/64 dev sit0  metric 256  expires 4481732sec mtu 1480 advmss 7140
>> hoplimit 4294967295 <-- wrong
>> fe80::/64 dev ppp0  metric 256  expires 19071334sec mtu 1500 advmss 7140
>> hoplimit 4294967295 <-- wrong
>> fe80::/64 dev eth0  metric 256  expires 19072419sec mtu 7200 advmss 7140
>> hoplimit 4294967295 <-- correct
>> 
>> Explicitly setting the MTU on these other routes (although this is not possible
>> without having to add another route due to bug 8755) automatically sets ADVMSS
>> appropriately.
>> 


-- 
Simon Arlott
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