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Old 05-28-2010, 09:49 PM
Per Lundberg
 
Default IPv4-capable XDMCP server in Debian squeeze?

Hi there!

Isn't there any XDMCP-capable server available in squeeze that can
speak ipv4 any more?

I read about the "net.ipv6.bindv6only" issue (in a bug report).
However, that setting is most assuredly set to 0 when I check with
sysctl -a.
I also forcibly disabled IPv6 support altogether (since I don't need
it), also by using a sysctl interface, but it still doesn't help me.

Both when trying with xdm and gdm, they *only* bind to the udp6
socket. Quite broken if you ask me, _especially when ipv6 support is
disabled in the kernel_!

I haven't tried with KDM so far (and I'd rather not, since I have no
interest in running KDE).

Any hints? The reason I want IPv4 XDMCP is that I will connect to the
server from a Windows XP machine, using Xming. I wasn't aware that
this has suddenly become an awful lot of work, since the introduction
of the wonderful new toy called IPv6... :-)

(Please, Cc any replies to my email address since I don't subscribe to
the mailing list. Thanks)
--
Best regards,
Per Lundberg


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Old 05-29-2010, 05:58 PM
Carl Johnson
 
Default IPv4-capable XDMCP server in Debian squeeze?

Per Lundberg <perlun@gmail.com> writes:

> Hi there!
>
> Isn't there any XDMCP-capable server available in squeeze that can
> speak ipv4 any more?
>
> I read about the "net.ipv6.bindv6only" issue (in a bug report).
> However, that setting is most assuredly set to 0 when I check with
> sysctl -a.
> I also forcibly disabled IPv6 support altogether (since I don't need
> it), also by using a sysctl interface, but it still doesn't help me.

It can't be binding to an interface that doesn't exist, so it sounds
as though you haven't disabled it properly. You can type
'/sbin/ifconfig' and look for inet6 entries. You shouldn't have any
if IPv6 is disabled. You can check for anything listening on IPv6
with 'netstat -l6'. Have you looked at the Debian wiki page at
'http://wiki.debian.org/DebianIPv6'? If you have followed those
directions for disabling, did you reboot afterwards?

> Both when trying with xdm and gdm, they *only* bind to the udp6
> socket. Quite broken if you ask me, _especially when ipv6 support is
> disabled in the kernel_!

I just looked at mine (kdm) and it only seems to be listening to IPv6,
but I am pretty sure it will also connect to IPv4. I just checked
google and there are some similar problems listed and some suggestions
on how to solve them. One suggests using module aliases to prevent
loading the IPv6 module
(http://www.linux.com/community/blogs/disable-ipv6-on-debian-lenny-quick-howto.html).

> I haven't tried with KDM so far (and I'd rather not, since I have no
> interest in running KDE).

I wouldn't expect it to be different.

> Any hints? The reason I want IPv4 XDMCP is that I will connect to the
> server from a Windows XP machine, using Xming. I wasn't aware that
> this has suddenly become an awful lot of work, since the introduction
> of the wonderful new toy called IPv6... :-)
>
> (Please, Cc any replies to my email address since I don't subscribe to
> the mailing list. Thanks)

Done.

--
Carl Johnson carlj@peak.org


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Old 05-29-2010, 07:32 PM
Per Lundberg
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 8:58 PM, Carl Johnson <carlj@peak.org> wrote:

Hi Carl, and thanks for your reply!

(I'll include my full original email, since I extended the audience to
the debian-devel list as well)

> Per Lundberg <perlun@gmail.com> writes:
>
>> Isn't there any XDMCP-capable server available in squeeze that can
>> speak ipv4 any more?
>>
>> I read about the "net.ipv6.bindv6only" issue (in a bug report).
>> However, that setting is most assuredly set to 0 when I check with
>> sysctl -a.
>> I also forcibly disabled IPv6 support altogether (since I don't need
>> it), also by using a sysctl interface, but it still doesn't help me.
> It can't be binding to an interface that doesn't exist, so it sounds
> as though you haven't disabled it properly. *You can type
> '/sbin/ifconfig' and look for inet6 entries. *You shouldn't have any
> if IPv6 is disabled. *You can check for anything listening on IPv6
> with 'netstat -l6'. *Have you looked at the Debian wiki page at
> 'http://wiki.debian.org/DebianIPv6'? *If you have followed those
> directions for disabling, did you reboot afterwards?

Yes, the sysctl thing from the Wiki page is exactly the same method
I'm using. I just rebooted, and this is the output from netstat -l6
afterwards:

per@terah:~$ netstat -l6
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp6 0 0 [::]:ssh [::]:* LISTEN
tcp6 0 0 [::]:microsoft-ds [::]:* LISTEN
tcp6 0 0 [::]:netbios-ssn [::]:* LISTEN
tcp6 0 0 [::]:57650 [::]:* LISTEN
udp6 0 0 [::]:xdmcp [::]:*

The sysctl is definitely in effect, though:

per@terah:/etc/sysctl.d$ /sbin/sysctl -a | grep ipv6 | grep disable
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth1.disable_ipv6 = 1
net.ipv6.conf.eth2.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1

...and ifconfig doesn't show any ipv6 addresses.

> I just looked at mine (kdm) and it only seems to be listening to IPv6,
> but I am pretty sure it will also connect to IPv4. *I just checked
> google and there are some similar problems listed and some suggestions
> on how to solve them. *One suggests using module aliases to prevent
> loading the IPv6 module
> (http://www.linux.com/community/blogs/disable-ipv6-on-debian-lenny-quick-howto.html).

Yeah, I read the idea about module aliases as well, but it seems
pointless since IPv6 isn't a module on my system (using the
2.6.32-3-amd64 kernel from squeeze).

It's interesting however that you say that you expect it to work with
IPv4 even though it has only bound the ipv6 socket. I guess you could
be right (depending on how the actual ipv4-to-ipv6 stuff works...). In
my case however, I can't get a working XMDCP login screen so I'm
suspecting this is the problem.

(Please, Cc any replies to my email address since I don't subscribe to
the mailing lists. Thanks)
--
Best regards,
Per Lundberg


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Old 05-29-2010, 07:32 PM
Per Lundberg
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 8:58 PM, Carl Johnson <carlj@peak.org> wrote:

Hi Carl, and thanks for your reply!

(I'll include my full original email, since I extended the audience to
the debian-devel list as well)

> Per Lundberg <perlun@gmail.com> writes:
>
>> Isn't there any XDMCP-capable server available in squeeze that can
>> speak ipv4 any more?
>>
>> I read about the "net.ipv6.bindv6only" issue (in a bug report).
>> However, that setting is most assuredly set to 0 when I check with
>> sysctl -a.
>> I also forcibly disabled IPv6 support altogether (since I don't need
>> it), also by using a sysctl interface, but it still doesn't help me.
> It can't be binding to an interface that doesn't exist, so it sounds
> as though you haven't disabled it properly. *You can type
> '/sbin/ifconfig' and look for inet6 entries. *You shouldn't have any
> if IPv6 is disabled. *You can check for anything listening on IPv6
> with 'netstat -l6'. *Have you looked at the Debian wiki page at
> 'http://wiki.debian.org/DebianIPv6'? *If you have followed those
> directions for disabling, did you reboot afterwards?

Yes, the sysctl thing from the Wiki page is exactly the same method
I'm using. I just rebooted, and this is the output from netstat -l6
afterwards:

per@terah:~$ netstat -l6
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp6 0 0 [::]:ssh [::]:* LISTEN
tcp6 0 0 [::]:microsoft-ds [::]:* LISTEN
tcp6 0 0 [::]:netbios-ssn [::]:* LISTEN
tcp6 0 0 [::]:57650 [::]:* LISTEN
udp6 0 0 [::]:xdmcp [::]:*

The sysctl is definitely in effect, though:

per@terah:/etc/sysctl.d$ /sbin/sysctl -a | grep ipv6 | grep disable
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth1.disable_ipv6 = 1
net.ipv6.conf.eth2.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1

...and ifconfig doesn't show any ipv6 addresses.

> I just looked at mine (kdm) and it only seems to be listening to IPv6,
> but I am pretty sure it will also connect to IPv4. *I just checked
> google and there are some similar problems listed and some suggestions
> on how to solve them. *One suggests using module aliases to prevent
> loading the IPv6 module
> (http://www.linux.com/community/blogs/disable-ipv6-on-debian-lenny-quick-howto.html).

Yeah, I read the idea about module aliases as well, but it seems
pointless since IPv6 isn't a module on my system (using the
2.6.32-3-amd64 kernel from squeeze).

It's interesting however that you say that you expect it to work with
IPv4 even though it has only bound the ipv6 socket. I guess you could
be right (depending on how the actual ipv4-to-ipv6 stuff works...). In
my case however, I can't get a working XMDCP login screen so I'm
suspecting this is the problem.

(Please, Cc any replies to my email address since I don't subscribe to
the mailing lists. Thanks)
--
Best regards,
Per Lundberg


--
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with a subject of "unsubscribe". Trouble? Contact listmaster@lists.debian.org
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Old 05-29-2010, 07:54 PM
Julien Cristau
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 22:32:07 +0300, Per Lundberg wrote:

> >> Isn't there any XDMCP-capable server available in squeeze that can
> >> speak ipv4 any more?

I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
squeeze, because I tested them (and made them work with the bindv6only=1
setting) a month or two ago.

Cheers,
Julien
 
Old 05-29-2010, 07:54 PM
Julien Cristau
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 22:32:07 +0300, Per Lundberg wrote:

> >> Isn't there any XDMCP-capable server available in squeeze that can
> >> speak ipv4 any more?

I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
squeeze, because I tested them (and made them work with the bindv6only=1
setting) a month or two ago.

Cheers,
Julien
 
Old 05-29-2010, 08:16 PM
Per Lundberg
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 10:54 PM, Julien Cristau <jcristau@debian.org> wrote:

Hi Julien,

> I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
> squeeze, because I tested them (and made them work with the bindv6only=1
> setting) a month or two ago.

OK, that's interesting... Just for the sake of it, I even tried
enabling the bindv6only (net.ipv6.bindv6only=1) setting, to see if it
would make any difference. Negative; it still only binds to the udp6
socket.

per@terah:/etc/sysctl.d$ sudo netstat -l -n -p | grep 177
udp6 0 0 :::177 :::*
1632/xdm

Do you have any active XDM setup where you could try this yourself? As
I hinted in my previous email, I'm not 100% sure of this, but doesn't
the above udp6 line mean that it will *only* work from an ipv6-capable
client...?
--
Best regards,
Per Lundberg


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Old 05-29-2010, 08:16 PM
Per Lundberg
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 10:54 PM, Julien Cristau <jcristau@debian.org> wrote:

Hi Julien,

> I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
> squeeze, because I tested them (and made them work with the bindv6only=1
> setting) a month or two ago.

OK, that's interesting... Just for the sake of it, I even tried
enabling the bindv6only (net.ipv6.bindv6only=1) setting, to see if it
would make any difference. Negative; it still only binds to the udp6
socket.

per@terah:/etc/sysctl.d$ sudo netstat -l -n -p | grep 177
udp6 0 0 :::177 :::*
1632/xdm

Do you have any active XDM setup where you could try this yourself? As
I hinted in my previous email, I'm not 100% sure of this, but doesn't
the above udp6 line mean that it will *only* work from an ipv6-capable
client...?
--
Best regards,
Per Lundberg


--
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Old 05-29-2010, 08:22 PM
Julien Cristau
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 23:16:06 +0300, Per Lundberg wrote:

> On Sat, May 29, 2010 at 10:54 PM, Julien Cristau <jcristau@debian.org> wrote:
>
> Hi Julien,
>
> > I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
> > squeeze, because I tested them (and made them work with the bindv6only=1
> > setting) a month or two ago.
>
> OK, that's interesting... Just for the sake of it, I even tried
> enabling the bindv6only (net.ipv6.bindv6only=1) setting, to see if it
> would make any difference. Negative; it still only binds to the udp6
> socket.
>
> per@terah:/etc/sysctl.d$ sudo netstat -l -n -p | grep 177
> udp6 0 0 :::177 :::*
> 1632/xdm
>
That's fine, bind() on in6addr_any lets you receive ipv4 packets when
IPV6_V6ONLY is turned off (which xdm does even if the system default is
backwards).

> Do you have any active XDM setup where you could try this yourself? As
> I hinted in my previous email, I'm not 100% sure of this, but doesn't
> the above udp6 line mean that it will *only* work from an ipv6-capable
> client...?

Sorry, I can't test right now, but no, as I said above an udp6 socket
can talk to ipv4 hosts.

Cheers,
Julien
 
Old 05-29-2010, 08:22 PM
Julien Cristau
 
Default IPv4-capable XDMCP server in Debian squeeze?

On Sat, May 29, 2010 at 23:16:06 +0300, Per Lundberg wrote:

> On Sat, May 29, 2010 at 10:54 PM, Julien Cristau <jcristau@debian.org> wrote:
>
> Hi Julien,
>
> > I'm fairly sure xdmcp over ipv4 works just fine with both xdm and gdm in
> > squeeze, because I tested them (and made them work with the bindv6only=1
> > setting) a month or two ago.
>
> OK, that's interesting... Just for the sake of it, I even tried
> enabling the bindv6only (net.ipv6.bindv6only=1) setting, to see if it
> would make any difference. Negative; it still only binds to the udp6
> socket.
>
> per@terah:/etc/sysctl.d$ sudo netstat -l -n -p | grep 177
> udp6 0 0 :::177 :::*
> 1632/xdm
>
That's fine, bind() on in6addr_any lets you receive ipv4 packets when
IPV6_V6ONLY is turned off (which xdm does even if the system default is
backwards).

> Do you have any active XDM setup where you could try this yourself? As
> I hinted in my previous email, I'm not 100% sure of this, but doesn't
> the above udp6 line mean that it will *only* work from an ipv6-capable
> client...?

Sorry, I can't test right now, but no, as I said above an udp6 socket
can talk to ipv4 hosts.

Cheers,
Julien
 

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