mind-boggling questions
Hi,
I have a few questions on the Linux bridge, and I would appreciate it if someone could answer them.
1. Why does a bridge have a MAC address? A bridge doesn't need a MAC address. I understand that a Linux box might offer more than a regular switch, and for that you need a MAC address. But the services should be provided by a new tap interface added to the bridge. I believe that the bridge should not even be shown by ifconfig.
2. Why does a bridge take the lowest MAC address of the interfaces connected to it?
3. When I send broadcast frames to a bridge interface (etherwake -b -i br0 00:00:00:00:00:00), the frames are received by the interfaces of the bridge. But when I send the frames to one of the interfaces, they are not broadcasted to other interfaces. I though that the bridge interface (br0) behaves the same as an interface added to the bridge, but I was mistaken. What are the differences?
Thanks,
Irek
Signature · 2 lines
Ireneusz (Irek) Szczesniak http://www.irkos.org
2011/4/25 Ireneusz Szcześniak <[email protected]>
Quoted 9 lines
Hi,
I have a few questions on the Linux bridge, and I would appreciate it if someone could answer them.
1. Why does a bridge have a MAC address? A bridge doesn't need a MAC address. I understand that a Linux box might offer more than a regular switch, and for that you need a MAC address. But the services should
Yes, Linux bridge needs mac address. Because linux works based on the
802.1D bridge
which has MAC relay entity, Spanning tree protocol entity. The bridge
required mac-address to communicate
with other bridges. For example to form a loop-free network
spanning-tree protocol in the bridges will communicate with
the bridges using BPDU, the bpdus carry the bridge address to identify
from which bridge we have received the BPDU.
If your bridge just acts as forwarding agent, then mac address is not
requried.
be provided by a new tap interface added to the bridge. I believe that
Quoted 2 lines
the bridge should not even be shown by ifconfig.
I am not familiar with tap interface, So ignoring it.
I agree with you that bridge should not be shown in ifconfig. Bridge
must come up when anyone of the bridge ports are up.
But in current implementation we have to issue ifconfig <bridge> up to
make the bridge up. As far as i see it is not required.
Hope someone can give more clarification and its purpose
Quoted 2 lines
2. Why does a bridge take the lowest MAC address of the interfaces
Quoted 2 lines
connected to it?
From 802.1D
7.12.5 Unique identification of a bridge
A unique 48-bit Universally Administered MAC Address, termed the
Bridge Address, shall be assigned to
each Bridge. The Bridge Address may be the individual MAC Address of
a Bridge Port, in which case, use
of the address of the lowest numbered Bridge Port (Port 1) is
recommended.
Quoted 22 lines
3. When I send broadcast frames to a bridge interface (etherwake -b -i br0 00:00:00:00:00:00), the frames are received by the interfaces of the bridge. But when I send the frames to one of the interfaces, they are not broadcasted to other interfaces. I though that the bridge interface (br0) behaves the same as an interface added to the bridge, but I was mistaken. What are the differences?
no idea
Thanks,
Irek--
Ireneusz (Irek) Szczesniak
http://www.irkos.org
_______________________________________________
Bridge mailing list
[email protected]
https://lists.linux-foundation.org/mailman/listinfo/bridge
Thanks, Sasikanth, for your response. Yes, I didn't realize that we need a MAC address for STP. Not 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.
Quoted 72 lines · Sasikanth V
2011/4/25 Ireneusz Szcześniak <[email protected] <mailto:[email protected]>>
Hi,
I have a few questions on the Linux bridge, and I would appreciate it if someone could answer them.
1. Why does a bridge have a MAC address? A bridge doesn't need a MAC address. I understand that a Linux box might offer more than a regular switch, and for that you need a MAC address. But the services should
Yes, Linux bridge needs mac address. Because linux works based on
the 802.1D bridge
which has MAC relay entity, Spanning tree protocol entity. The
bridge required mac-address to communicate
with other bridges. For example to form a loop-free network
spanning-tree protocol in the bridges will communicate with
the bridges using BPDU, the bpdus carry the bridge address to
identify from which bridge we have received the BPDU.
If your bridge just acts as forwarding agent, then mac address is
not requried.be provided by a new tap interface added to the bridge. I believe that the bridge should not even be shown by ifconfig.
I am not familiar with tap interface, So ignoring it. I agree with you that bridge should not be shown in ifconfig.
Bridge must come up when anyone of the bridge ports are up.
But in current implementation we have to issue ifconfig <bridge>
up to make the bridge up. As far as i see it is not required.
Hope someone can give more clarification and its purpose2. Why does a bridge take the lowest MAC address of the interfaces connected to it?
From 802.1D
7.12.5 Unique identification of a bridge
A unique 48-bit Universally Administered MAC Address, termed the
Bridge Address, shall be assigned to
each Bridge. The Bridge Address may be the individual MAC
Address of a Bridge Port, in which case, use
of the address of the lowest numbered Bridge Port (Port 1) is
recommended.3. When I send broadcast frames to a bridge interface (etherwake -b -i br0 00:00:00:00:00:00), the frames are received by the interfaces of the bridge. But when I send the frames to one of the interfaces, they are not broadcasted to other interfaces. I though that the bridge interface (br0) behaves the same as an interface added to the bridge, but I was mistaken. What are the differences?
no idea
Thanks,
Irek--
Ireneusz (Irek) Szczesniak
http://www.irkos.org
_______________________________________________
Bridge mailing list
[email protected]
<mailto:[email protected]>
https://lists.linux-foundation.org/mailman/listinfo/bridge
Signature · 2 lines
Ireneusz (Irek) Szczesniak http://www.irkos.org
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 Szcześniak <[email protected]>:
Quoted 88 lines
Thanks, Sasikanth, for your response. Yes, I didn't realize that we need a MAC address for STP. Not 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.
Quoted 63 lines · Sasikanth V
2011/4/25 Ireneusz Szcześniak <[email protected] <mailto:[email protected]>>
Hi,
I have a few questions on the Linux bridge, and I would appreciate it if someone could answer them.
1. Why does a bridge have a MAC address? A bridge doesn't need a MAC address. I understand that a Linux box might offer more than a regular switch, and for that you need a MAC address. But the services should
Yes, Linux bridge needs mac address. Because linux works based on the 802.1D bridge
which has MAC relay entity, Spanning tree protocol entity. The bridge required mac-address to communicate
with other bridges. For example to form a loop-free network spanning-tree protocol in the bridges will communicate with the bridges using BPDU, the bpdus carry the bridge address to identify from which bridge we have received the BPDU.
If your bridge just acts as forwarding agent, then mac address is not requried.be provided by a new tap interface added to the bridge. I believe that the bridge should not even be shown by ifconfig.
I am not familiar with tap interface, So ignoring it. I agree with you that bridge should not be shown in ifconfig. Bridge must come up when anyone of the bridge ports are up. But in current implementation we have to issue ifconfig <bridge> up to make the bridge up. As far as i see it is not required. Hope someone can give more clarification and its purpose
2. Why does a bridge take the lowest MAC address of the interfaces connected to it?
From 802.1D
7.12.5 Unique identification of a bridge
A unique 48-bit Universally Administered MAC Address, termed the Bridge Address, shall be assigned to
each Bridge. The Bridge Address may be the individual MAC Address of a Bridge Port, in which case, use
of the address of the lowest numbered Bridge Port (Port 1) is recommended.3. When I send broadcast frames to a bridge interface (etherwake -b -i br0 00:00:00:00:00:00), the frames are received by the interfaces of the bridge. But when I send the frames to one of the interfaces, they are not broadcasted to other interfaces. I though that the bridge interface (br0) behaves the same as an interface added to the bridge, but I was mistaken. What are the differences?
no idea
Thanks,
IrekQuoted 9 lines
--
Ireneusz (Irek) Szczesniak
http://www.irkos.org
_______________________________________________
Bridge mailing list
[email protected]
<mailto:[email protected]>
https://lists.linux-foundation.org/mailman/listinfo/bridge--
Ireneusz (Irek) Szczesniak
http://www.irkos.org
_______________________________________________
Bridge mailing list
[email protected]
https://lists.linux-foundation.org/mailman/listinfo/bridge