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Old 09-05-2011, 12:10 PM
Steven
 
Default how to change mac address back after decnet changed it?

Dear Debian users,

Some time ago, an update on my wheezy system brought in dnet-common and
some related packages. I noticed that decnet changes the hardware
address of my interfaces, but didn't pay much attention to it, figuring
they would at least be unique, so I could fix up dhcp later. Having a
different IP for some time isn't all that bad in my setup.
However now I noticed that these hardware addresses are certainly NOT
unique. I have a machine with 2 NICs and both have aa:00:04:00:0a:04 as
hardware address (second one isn't plugged in physically), so is the
eth0 interface on my laptop. This obviously can't be right.
I already uninstalled the dnet-common package from 1 machine, but to no
effect after rebooting. It's neither an option when reconfiguring the
dnet-common package.

So how do I get rid of that aa:00:04:00:0a:04 address? And getting the
old ones back, note that I do not remember the old ones, nor do I have
them all written out somewhere.

This is getting pretty troublesome, as my DHCP server uses mac addresses
to always give the same IP to some machines on the network, (keeping
config centralized, but static IP to allow port forwarding).

Any help appreciated.

Kind regards,
Steven
 
Old 09-05-2011, 12:29 PM
Darac Marjal
 
Default how to change mac address back after decnet changed it?

On Mon, Sep 05, 2011 at 02:10:11PM +0200, Steven wrote:
> Dear Debian users,
>
> Some time ago, an update on my wheezy system brought in dnet-common and
> some related packages. I noticed that decnet changes the hardware
> address of my interfaces, but didn't pay much attention to it, figuring
> they would at least be unique, so I could fix up dhcp later. Having a
> different IP for some time isn't all that bad in my setup.
> However now I noticed that these hardware addresses are certainly NOT
> unique. I have a machine with 2 NICs and both have aa:00:04:00:0a:04 as
> hardware address (second one isn't plugged in physically), so is the
> eth0 interface on my laptop. This obviously can't be right.
> I already uninstalled the dnet-common package from 1 machine, but to no
> effect after rebooting. It's neither an option when reconfiguring the
> dnet-common package.

According to wikipedia[1], this is a feature, not a bug:
| The Ethernet implementation was unusual in that the software changed
| the physical address of the Ethernet interface on the network to
| AA-00-04-00-xx-yy where xx-yy reflected the DECnet network address of
| the host. This allowed ARP-less LAN operation because the LAN address
| could be deduced from the DECnet address. This precluded connecting two
| NICs from the same DECnet node onto the same LAN segment, however.

So your DECnet address would be 0x0A04.


>
> So how do I get rid of that aa:00:04:00:0a:04 address? And getting the
> old ones back, note that I do not remember the old ones, nor do I have
> them all written out somewhere.

You should be able to set the address with:
$ ifconfig ethN hw ether aa:bb:cc:dd:ee:ff

The value of the address doesn't really matter so long as it's unique on
your ethernet segment (i.e. your network). Then again, if you're doing
some sort of bonding or balancing, it doesn't even have to be unique.


[1] http://www.wikipedia.org/wiki/DECnet

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Darac Marjal


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Old 09-05-2011, 12:41 PM
Tom H
 
Default how to change mac address back after decnet changed it?

On Mon, Sep 5, 2011 at 8:10 AM, Steven <redalert.commander@gmail.com> wrote:
>
> Some time ago, an update on my wheezy system brought in dnet-common and
> some related packages. I noticed that decnet changes the hardware
> address of my interfaces, but didn't pay much attention to it, figuring
> they would at least be unique, so I could fix up dhcp later. Having a
> different IP for some time isn't all that bad in my setup.
> However now I noticed that these hardware addresses are certainly NOT
> unique. I have a machine with 2 NICs and both have aa:00:04:00:0a:04 as
> hardware address (second one isn't plugged in physically), so is the
> eth0 interface on my laptop. This obviously can't be right.
> I already uninstalled the dnet-common package from 1 machine, but to no
> effect after rebooting. It's neither an option when reconfiguring the
> dnet-common package.
>
> So how do I get rid of that aa:00:04:00:0a:04 address? And getting the
> old ones back, note that I do not remember the old ones, nor do I have
> them all written out somewhere.
>
> This is getting pretty troublesome, as my DHCP server uses mac addresses
> to always give the same IP to some machines on the network, (keeping
> config centralized, but static IP to allow port forwarding).

It's probably hard-wired the MAC into the udev rules. Move
"/etc/udev/rules/70-persistent-net.rules" out and reboot (there's
probably a way of regenerating it with udevadm but I don't know it).
It'll be regenerated with your original MACs. You can diff the old and
new to be sure.


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Old 09-05-2011, 01:56 PM
Brian
 
Default how to change mac address back after decnet changed it?

On Mon 05 Sep 2011 at 08:41:39 -0400, Tom H wrote:

> It's probably hard-wired the MAC into the udev rules. Move
> "/etc/udev/rules/70-persistent-net.rules" out and reboot (there's
> probably a way of regenerating it with udevadm but I don't know it).
> It'll be regenerated with your original MACs. You can diff the old and
> new to be sure.

For eth0

echo add > /sys/class/net/eth0/uevent

would be sufficient.


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Old 09-05-2011, 02:58 PM
Steven
 
Default how to change mac address back after decnet changed it?

On Mon, 2011-09-05 at 13:29 +0100, Darac Marjal wrote:
[...snip...]
>
> According to wikipedia[1], this is a feature, not a bug:
> | The Ethernet implementation was unusual in that the software changed
> | the physical address of the Ethernet interface on the network to
> | AA-00-04-00-xx-yy where xx-yy reflected the DECnet network address of
> | the host. This allowed ARP-less LAN operation because the LAN address
> | could be deduced from the DECnet address. This precluded connecting two
> | NICs from the same DECnet node onto the same LAN segment, however.
>
> So your DECnet address would be 0x0A04.

I imagine this confuses many network switches when unsuspecting users
pulled in these updates?

>
>
> >
> > So how do I get rid of that aa:00:04:00:0a:04 address? And getting the
> > old ones back, note that I do not remember the old ones, nor do I have
> > them all written out somewhere.
>
> You should be able to set the address with:
> $ ifconfig ethN hw ether aa:bb:cc:dd:ee:ff
>
> The value of the address doesn't really matter so long as it's unique on
> your ethernet segment (i.e. your network). Then again, if you're doing
> some sort of bonding or balancing, it doesn't even have to be unique.

Thanks, I was able to find the old hw addresses
in /etc/udev/rules.d/70-persistent-net.rule (thanks Tom H for the tip),
unfortunately the ifconfig method does not persist after reboot.
And I doubt the method Tom H suggested would work since the old address
is still in the udev file, not the new decnet address.

Why would one want to have this actually? Personally I don't see the
advantage it gives me over my existing network configuration using
mostly tcp/ip over ethernet. Just curious. Also according to the
wikipedia link you gave, decnet code in the kernel was orphaned with
2.6.33, I don't know if that is still the case.

Kind regards,
Steven
 
Old 09-05-2011, 03:22 PM
Brian
 
Default how to change mac address back after decnet changed it?

On Mon 05 Sep 2011 at 16:58:02 +0200, Steven wrote:

> Thanks, I was able to find the old hw addresses
> in /etc/udev/rules.d/70-persistent-net.rule (thanks Tom H for the tip),
> unfortunately the ifconfig method does not persist after reboot.
> And I doubt the method Tom H suggested would work since the old address
> is still in the udev file, not the new decnet address.

hwaddress is in interfaces(5). It might help.


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Old 09-05-2011, 04:24 PM
Steven
 
Default how to change mac address back after decnet changed it?

On Mon, 2011-09-05 at 16:22 +0100, Brian wrote:
> On Mon 05 Sep 2011 at 16:58:02 +0200, Steven wrote:
>
> > Thanks, I was able to find the old hw addresses
> > in /etc/udev/rules.d/70-persistent-net.rule (thanks Tom H for the tip),
> > unfortunately the ifconfig method does not persist after reboot.
> > And I doubt the method Tom H suggested would work since the old address
> > is still in the udev file, not the new decnet address.
>
> hwaddress is in interfaces(5). It might help.
>

Of course, I almost forgot about /etc/network/interfaces
Thanks a lot.

Kind regards,
Steven
 
Old 09-05-2011, 06:48 PM
Bob Proulx
 
Default how to change mac address back after decnet changed it?

Steven wrote:
> Some time ago, an update on my wheezy system brought in dnet-common and
> some related packages. I noticed that decnet changes the hardware
> address of my interfaces, but didn't pay much attention to it, figuring

I originally reported this as Bug#608807 back in January when I hit it.

libdnet: Only suggest dnet-common package
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=608807

And this is another bug report on it.

dnet-common: Do not change MAC addresses unless user chooses to configure DECnet
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=637179

Bob
 
Old 09-09-2011, 11:58 PM
Tom H
 
Default how to change mac address back after decnet changed it?

On Mon, Sep 5, 2011 at 3:56 PM, Brian <ad44@cityscape.co.uk> wrote:
> On Mon 05 Sep 2011 at 08:41:39 -0400, Tom H wrote:
>>>
>> It's probably hard-wired the MAC into the udev rules. Move
>> "/etc/udev/rules/70-persistent-net.rules" out and reboot (there's
>> probably a way of regenerating it with udevadm but I don't know it).
>> It'll be regenerated with your original MACs. You can diff the old and
>> new to be sure.
>
> For eth0
>
> * echo add > /sys/class/net/eth0/uevent
>
> would be sufficient.

Thanks.


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