Re: mind-boggling questions

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It is normal for switch vendors to assign mac addresses to a bridge -
only cheap consumer bridges don't have them, normally this is assigned
by a stanza during config.

I think many of these problems come from the fact that bridge devices
in linux are really more like a SAP construct. It would be more useful
IMHO to introduce a new class of "bridge" device which acted like a
SAP (service access port)

Consider:


Customer A - CVLAN 100
Customer B - CVLAN 200

Service A - SVLAN 1000
Service B - SVLAN 2000

Incoming interface received QinQ (stacked) 1000:[100-200] as both
subscribers are on service 1000.

To get both of these customers to be in the same segment you first
need to create a bridge, create a vlan 1000, then each CVLAN per
customer off this new interface, and finally add it to the bridge.

Tunable  like per bridge member interface broadcast enable/disable etc
would be nice as well.

A SAP construct would allow alot more flexibility and I think clear up
some of the uses that bridge devices are currently used for.



2011/4/26 Ireneusz SzczeÅniak <irek.szczesniak@xxxxxxxxx>:
> Thanks, Sasikanth, for your response. ÂYes, I didn't realize that we
> need a MAC address for STP. ÂNot only we need a MAC for a bridge, but
> there can be MAC addresses for ports too, and why I just don't know.
> I need to do some reading on STP, because I know very little about it.
>
> On 25.04.2011 13:02, Sasikanth V wrote:
>> 2011/4/25 Ireneusz SzczeÅniak <irek.szczesniak@xxxxxxxxx
>> <mailto:irek.szczesniak@xxxxxxxxx>>
>>
>> Â Â Hi,
>>
>> Â Â I have a few questions on the Linux bridge, and I would appreciate it
>> Â Â if someone could answer them.
>>
>> Â Â 1. Why does a bridge have a MAC address? ÂA bridge doesn't need a MAC
>> Â Â address. I understand that a Linux box might offer more than a regular
>> Â Â switch, and for that you need a MAC address. But the services should
>>
>> Â Â ÂYes, Linux bridge needs mac address. Because linux works based on
>> the 802.1D bridge
>> Â Â Âwhich has MAC relay entity, ÂSpanning tree protocol entity. The
>> bridge required mac-address to communicate
>> Â Â Âwith other bridges. For example to form a loop-free network
>> spanning-tree protocol in the bridges will communicate with
>> Â Â Âthe bridges using BPDU, the bpdus carry the bridge address to
>> identify from which bridge we have received the BPDU.
>> Â Â ÂIf your bridge just acts as forwarding Âagent, then mac address is
>> not requried.
>>
>> Â Â be provided by a new tap interface added to the bridge. I believe that
>> Â Â the bridge should not even be shown by ifconfig.
>>
>>
>> Â Â ÂI am not familiar with tap interface, So ignoring it.
>> Â Â ÂI agree with you that bridge should not be shown in ifconfig.
>> Bridge must come up Âwhen anyone of the bridge ports are up.
>> Â Â ÂBut in current implementation we have to issue ifconfig <bridge>
>> up Âto make the bridge up. As far as i see it is not required.
>> Â Â ÂHope someone can give more clarification and its purpose
>>
>>
>> Â Â 2. Why does a bridge take the lowest MAC address of the interfaces
>> Â Â connected to it?
>>
>>
>> Â Â Â Â From 802.1D
>>
>> Â Â Â Â 7.12.5 Unique identification of a bridge
>> Â Â Â Â A unique 48-bit Universally Administered MAC Address, termed the
>> Bridge Address, shall be assigned to
>> Â Â Â Â each Bridge. The Bridge Address may be the individual MAC
>> Address of a Bridge Port, in which case, use
>> Â Â Â Â of the address of the lowest numbered Bridge Port (Port 1) is
>> recommended.
>>
>>
>> Â Â 3. When I send broadcast frames to a bridge interface (etherwake -b -i
>> Â Â br0 00:00:00:00:00:00), the frames are received by the interfaces of
>> Â Â the bridge. ÂBut when I send the frames to one of the interfaces, they
>> Â Â are not broadcasted to other interfaces. ÂI though that the bridge
>> Â Â interface (br0) behaves the same as an interface added to the bridge,
>> Â Â but I was mistaken. ÂWhat are the differences?
>>
>> Â Â Âno idea
>>
>>
>> Â Â Thanks,
>> Â Â Irek
>>
>> Â Â --
>> Â Â Ireneusz (Irek) Szczesniak
>> Â Â http://www.irkos.org
>> Â Â _______________________________________________
>> Â Â Bridge mailing list
>> Â Â Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> Â Â <mailto:Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx>
>> Â Â https://lists.linux-foundation.org/mailman/listinfo/bridge
>>
>
>
> --
> Ireneusz (Irek) Szczesniak
> http://www.irkos.org
> _______________________________________________
> Bridge mailing list
> Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx
> https://lists.linux-foundation.org/mailman/listinfo/bridge
>
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