Xen users - Jun 2009 - bridge interface with (initially) no ports

I use some completely virtual networks inside my DomU''s. In Dom0 I want
to have the following in /etc/network/interfaces:

auto br-wan
iface br-wan inet static
 address x.y.z.254
 netmask 255.255.255.0
 bridge_maxwait 0
 bridge_ports none
up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE

but of course when the br-wan interface comes up, it has no mac address
because it has no ports yet to inherit a mac address from.

I am working around it for now by using a dummy interface:

auto br-wan
iface br-wan inet static
address x.y.z.254 netmask 255.255.255.0
 bridge_maxwait 0
 bridge_ports dummy1
 bridge_hw 00:1a:4b:eb:ee:7c
 up ip addr add 2002:xy:zfe:3::1/64 dev $IFACE

but is there a better way? The dummy module in the kernel needs a
parameter passed to it to set the number of dummy interfaces, and if I
ever need to increase it I have to unload and reload it which means
downing all the bridge interfaces that use it. Not really what I want.

It''s just occurred to me while writing this that I could vlan the dummy
interface and just use the one interface but still... seems a bit of a
kludge.

Thanks

James


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On Sat, Jun 27, 2009 at 9:50 AM, James
Harper<james.harper@bendigoit.com.au> wrote:
> I use some completely virtual networks inside my DomU''s. In Dom0 I
want
> to have the following in /etc/network/interfaces:
>
> auto br-wan
> iface br-wan inet static
>  address x.y.z.254
>  netmask 255.255.255.0
>  bridge_maxwait 0
>  bridge_ports none
> up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE
>
> but of course when the br-wan interface comes up, it has no mac address
> because it has no ports yet to inherit a mac address from.
Here''s what I get on my Ubuntu
# brctl addbr br-test1
# ip link show br-test1
12: br-test1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
    link/ether ea:32:77:5d:2d:f7 brd ff:ff:ff:ff:ff:ff

it has a mac address by default.

Even if it doesn''t have a mac address, you should be able to assign one
# ip link set br-test1 addr 00:16:3e:00:00:01
# ip link show br-test1
12: br-test1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
    link/ether 00:16:3e:00:00:01 brd ff:ff:ff:ff:ff:ff

-- 
Fajar

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"James Harper" <james.harper@bendigoit.com.au> writes:
> auto br-wan
> iface br-wan inet static
>  address x.y.z.254
>  netmask 255.255.255.0
  hwaddress ether xx:xx:xx:xx:xx:xx
>  bridge_maxwait 0
>  bridge_ports none
> up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE
>
> but of course when the br-wan interface comes up, it has no mac address
> because it has no ports yet to inherit a mac address from.
Try adding the line above.
-- 
Feri.

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> 
> > auto br-wan
> > iface br-wan inet static
> >  address x.y.z.254
> >  netmask 255.255.255.0
>   hwaddress ether xx:xx:xx:xx:xx:xx
> >  bridge_maxwait 0
> >  bridge_ports none
> > up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE
> >
> > but of course when the br-wan interface comes up, it has no mac
address
> > because it has no ports yet to inherit a mac address from.
> 
> Try adding the line above.
SIOCSIFHWADDR: Cannot assign requested address

I can''t set a hardware address on a bridge, that''s the whole
problem.

James

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"James Harper" <james.harper@bendigoit.com.au> writes:
>>> auto br-wan
>>> iface br-wan inet static
>>>  address x.y.z.254
>>>  netmask 255.255.255.0
>>   hwaddress ether xx:xx:xx:xx:xx:xx
>>>  bridge_maxwait 0
>>>  bridge_ports none
>>> up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE
>>>
>>> but of course when the br-wan interface comes up, it has no mac
>>> address because it has no ports yet to inherit a mac address from.
>> 
>> Try adding the line above.
>
> SIOCSIFHWADDR: Cannot assign requested address
>
> I can''t set a hardware address on a bridge, that''s the
whole problem.
Maybe you want to assign a multicast address.  Ensure that the first
octet is even (ie. 11:22:33:44:55:66 won''t work, 12:22:33:44:55:66
should).  This works for me.
-- 
Feri.

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> "James Harper" <james.harper@bendigoit.com.au> writes:
> 
> >>> auto br-wan
> >>> iface br-wan inet static
> >>>  address x.y.z.254
> >>>  netmask 255.255.255.0
> >>   hwaddress ether xx:xx:xx:xx:xx:xx
> >>>  bridge_maxwait 0
> >>>  bridge_ports none
> >>> up ip addr add 2002:xy:xfe:3::1/64 dev $IFACE
> >>>
> >>> but of course when the br-wan interface comes up, it has no
mac
> >>> address because it has no ports yet to inherit a mac address
from.
> >>
> >> Try adding the line above.
> >
> > SIOCSIFHWADDR: Cannot assign requested address
> >
> > I can''t set a hardware address on a bridge, that''s
the whole
problem.
> 
> Maybe you want to assign a multicast address.  Ensure that the first
> octet is even (ie. 11:22:33:44:55:66 won''t work, 12:22:33:44:55:66
> should).  This works for me.
I have been using 00:00:01:02:03:04

James

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