IPv4 socket bind using IPv6 socket on openjdk6 breaks udp send

Matthias Andree matthias.andree at gmx.de
Mon Jun 27 11:17:06 UTC 2011

Am 25.06.2011 13:28, schrieb Steven Hartland:
> ----- Original Message ----- From: "Matthias Andree"
> <matthias.andree at gmx.de>
> I'm adding back in -java as based on you comments it may well be
> something in the jdk passing invalid values down to the kernel
> syscall.
>>> The socket bind works fine and the packets sent to the server arrive
>>> and are processed by the app but when it tries to reply using
>>> send the result is:-
>>> java.io.IOException: Invalid argument
>>>        at java.net.PlainDatagramSocketImpl.send(Native Method)
>>>        at java.net.DatagramSocket.send(DatagramSocket.java:629)
>>> using truss we see the following:-
>>> socket(PF_INET6,SOCK_DGRAM,0)            = 20 (0x14)
>>> setsockopt(0x14,0x29,0x1b,0x7ffffedf0318,0x4,0x0) = 0 (0x0)
>>> setsockopt(0x14,0xffff,0x20,0x7ffffedf031c,0x4,0x0) = 0 (0x0)
>>> bind(20,{ AF_INET6 [3800::10:0:0:0]:20736 },28)  = 0 (0x0)
>>> ..
>>> sendto(20,"\M^?\M^?\M^?\M^?I\aMultiplay :: "...,82,0x0,{ AF_INET6
>>> [3800::10:0:0:0]:20736 },0x1c) ERR#22 'Invalid argument'
>> You're trying to send to your own address, but you're likely not using
>> the loopback interface for that.  Is that permitted by your firewall
>> configuration and routing?
> No I'm not its replying to the sender. 

Yes you are, check your trace: The sendto address and port are the same
as the bound address.

> In the java code we have:-
> socket.send( new DatagramPacket( data, data.length,
> src.getSocketAddress() ) );
> Where src is the src packet. This works fine on IPv4 only machines and
> when the jdk is told to use only IPv4 stack. So its not a problem with
> the java code itself but could well be an issue with the

What data type is it?

>>> sockstat shows it binding correctly
>>> root     java       894   21 tcp4  *:*
>> This is unrelated, as it has fd #21 not #20 as in the socket/bind/sendto
>> calls.  You've quoted the wrong line from sockstat output.
> Oops sorry cut and paste error (wrong line) heres the correct line.
> root     java       894   20 udp4  *:*

While a datagram socket, it does not match the socket()/bind() above.

An INET6-domain datagram socket would be listed as udp6 here.  Are you
sure you're tracing the right VM and are looking at the right thread?

If so, is the incriminated traffic actually going through socket #20?

Is src.getSocketAddress() actually returning an IPv6 address?
SocketAddress is an abstract class. For my lack of Java knowledge: are
there any automatic type promotions on the Java side?

What's the Java code for binding to the socket and fetching the query

> The jvm automatically sets this on all sockets for compatibility for
> this exact reason. I'm not rulling out an issue with the IPv6 -> v4
> routing in the kernel though.

That is prohibited, so there isn't IPv6 -> IPv4 routing. All IPv6
traffic remains in the IPv6 domain.

>> Are you sure that's what you seeing?  It's not a match for what you give
>> above, but anyways it's an implementation artifact because the tcp code
>> for v4 and v6 used to be shared and the udp code separate.
> Thats not how the jdk works, its ment to be 100% transparent but isn't.

You mean the JRE.

>> It is best to set up one IPv4 and one IPv6 listening socket.
> I don't believe there is any way to do this in java it either uses the
> IPv4 stack only or the IPv6 stack only hence relies on the kernel
> routing IPv4 packets through the IPv6 stack.
> Thats the reason the jdk explicitly enables this for all the ports it
> creates, which was added as a back port of the jdk7 fixes which can
> be seen here:-
> http://www.freebsd.org/cgi/cvsweb.cgi/ports/java/openjdk6/files/patch-set
>> Check the URL above, perhaps that helps your understanding a bit.  I
>> presume 3800::10:0:0:0 is your server?
> Not that I'm aware of, here's the output from ifconfig if anyone can
> tell me different, as I'm new to IPv6 and don't follow how its mapped
> yet.
> ifconfig
> igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>        ether 00:25:90:2c:3c:b0
>        inet netmask 0xffffff00 broadcast
>        inet6 fe80::225:90ff:fe2c:3cb0%igb0 prefixlen 64 scopeid 0x1
>        inet6 2001:4db0:20:2::1337 prefixlen 64        nd6

The 2001:something is your local address. If you bind to 3800::
something that won't work.  You couldn't bind an IPv4 address of on this interface either.

> igb1: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500
>        ether 00:25:90:2c:3c:b1
>        media: Ethernet autoselect (1000baseSX <full-duplex>)
>        status: active

This iface has no addresses at IP level at all.

> lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
>        options=3<RXCSUM,TXCSUM>
>        inet netmask 0xff000000        
>        inet6 ::1 prefixlen 128
>        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3        nd6

Other than that, looks reasonable. There are link-local IPv6 addresses
on igb0 and lo0, and there is a global IPv6 address on igb0. There is a
routable IPv4 address on igb0, and the loopback address on lo0. That's
OK, but an IPv6 bind could only ever use an address from
2001:4db0:20:2::/64, not 3800.

Are you sure you're using the right address in bind()? It specifies the
local sender address for transmitted datagrams...

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