* Re: [Bugme-new] [Bug 42372] New: routing table cache entries lose mtu/advmss attributes
[not found] <bug-42372-10286@https.bugzilla.kernel.org/>
@ 2011-09-07 21:32 ` Andrew Morton
0 siblings, 0 replies; only message in thread
From: Andrew Morton @ 2011-09-07 21:32 UTC (permalink / raw)
To: netdev; +Cc: bugzilla-daemon, bugme-daemon, david+bugs
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On Sun, 4 Sep 2011 18:45:16 GMT
bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=42372
>
> Summary: routing table cache entries lose mtu/advmss attributes
> Product: Networking
> Version: 2.5
> Kernel Version: 3.0.4
> Platform: All
> OS/Version: Linux
> Tree: Mainline
> Status: NEW
> Severity: normal
> Priority: P1
> Component: IPV6
> AssignedTo: yoshfuji@linux-ipv6.org
> ReportedBy: david+bugs@madore.org
> Regression: Yes
>
>
> To reproduce: create a static IPv6 route with a specific mtu/advmss attribute,
> then open a TCP connection to a host (never contacted before) within this
> route: this creates a cache entry with additional information (such as rtt);
> when these data expire, the route mtu/advmss are also forgotten, even though
> they are specified in the (static) routing table.
>
> E.g. (using www.kame.net = 2001:200:dff:fff1:216:3eff:feb1:44d7 as example):
>
> david@terre:~$ sudo ip route get 2001:200:dff:fff1:216:3eff:feb1:44d7
> 2001:200:dff:fff1:216:3eff:feb1:44d7 from :: via fe80::20e:a6ff:fef1:db7f dev
> eth0 src 2001:7a8:78ae:37:21f:c6ff:fec1:c877 metric 0
> cache
> david@terre:~$ sudo ip route add 2001:200:dff:fff1::/64 from :: via
> fe80::20e:a6ff:fef1:db7f dev eth0 src 2001:7a8:78ae:37:21f:c6ff:fec1:c877 mtu
> 1460 advmss 1400
> david@terre:~$ sudo ip route get 2001:200:dff:fff1:216:3eff:feb1:44d7
> 2001:200:dff:fff1:216:3eff:feb1:44d7 from :: via fe80::20e:a6ff:fef1:db7f dev
> eth0 src 2001:7a8:78ae:37:21f:c6ff:fec1:c877 metric 0
> cache mtu 1460 advmss 1400
> david@terre:~$ wget -O /dev/null
> 'http://[2001:200:dff:fff1:216:3eff:feb1:44d7]/'
> (...)
> david@terre:~$ sudo ip route get 2001:200:dff:fff1:216:3eff:feb1:44d7
> 2001:200:dff:fff1:216:3eff:feb1:44d7 from :: via fe80::20e:a6ff:fef1:db7f dev
> eth0 src 2001:7a8:78ae:37:21f:c6ff:fec1:c877 metric 0
> cache mtu 1460 rtt 324ms rttvar 324ms cwnd 10 advmss 1400 hoplimit 255
> david@terre:~$ sleep 30
> david@terre:~$ sudo ip route get 2001:200:dff:fff1:216:3eff:feb1:44d7
> 2001:200:dff:fff1:216:3eff:feb1:44d7 from :: via fe80::20e:a6ff:fef1:db7f dev
> eth0 src 2001:7a8:78ae:37:21f:c6ff:fec1:c877 metric 0
> cache hoplimit 64
>
> In the last output, the mtu and advmss for the route have been forgotten, even
> though the route is still supposed to be active. This is not just the output
> of "ip" which is bad: actually opening a TCP connection at this point will use
> a wrong MSS.
>
> A similar bug might be present in IPv4 routes, but I found it trickier to
> reproduce, so I'm not entirely sure whether this is really an IPv6-related
> problem.
>
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