* [Bridge] mind-boggling questions @ 2011-04-25 9:37 Ireneusz Szcześniak 2011-04-25 11:02 ` Sasikanth V 0 siblings, 1 reply; 4+ messages in thread From: Ireneusz Szcześniak @ 2011-04-25 9:37 UTC (permalink / raw) To: bridge 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 -- Ireneusz (Irek) Szczesniak http://www.irkos.org ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Bridge] mind-boggling questions 2011-04-25 9:37 [Bridge] mind-boggling questions Ireneusz Szcześniak @ 2011-04-25 11:02 ` Sasikanth V 2011-04-25 18:32 ` Ireneusz Szcześniak 0 siblings, 1 reply; 4+ messages in thread From: Sasikanth V @ 2011-04-25 11:02 UTC (permalink / raw) To: Ireneusz Szcześniak; +Cc: bridge [-- Attachment #1: Type: text/plain, Size: 2635 bytes --] 2011/4/25 Ireneusz Szcześniak <irek.szczesniak@gmail.com> > 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, > Irek > > -- > Ireneusz (Irek) Szczesniak > http://www.irkos.org > _______________________________________________ > Bridge mailing list > Bridge@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/bridge > [-- Attachment #2: Type: text/html, Size: 4005 bytes --] ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Bridge] mind-boggling questions 2011-04-25 11:02 ` Sasikanth V @ 2011-04-25 18:32 ` Ireneusz Szcześniak 2011-04-25 20:43 ` Joel Wiramu Pauling 0 siblings, 1 reply; 4+ messages in thread From: Ireneusz Szcześniak @ 2011-04-25 18:32 UTC (permalink / raw) To: 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. On 25.04.2011 13:02, Sasikanth V wrote: > 2011/4/25 Ireneusz Szcześniak <irek.szczesniak@gmail.com > <mailto:irek.szczesniak@gmail.com>> > > 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, > Irek > > -- > Ireneusz (Irek) Szczesniak > http://www.irkos.org > _______________________________________________ > Bridge mailing list > Bridge@lists.linux-foundation.org > <mailto:Bridge@lists.linux-foundation.org> > https://lists.linux-foundation.org/mailman/listinfo/bridge > -- Ireneusz (Irek) Szczesniak http://www.irkos.org ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Bridge] mind-boggling questions 2011-04-25 18:32 ` Ireneusz Szcześniak @ 2011-04-25 20:43 ` Joel Wiramu Pauling 0 siblings, 0 replies; 4+ messages in thread From: Joel Wiramu Pauling @ 2011-04-25 20:43 UTC (permalink / raw) To: Ireneusz Szcześniak; +Cc: bridge 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 <irek.szczesniak@gmail.com>: > 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. > > On 25.04.2011 13:02, Sasikanth V wrote: >> 2011/4/25 Ireneusz Szcześniak <irek.szczesniak@gmail.com >> <mailto:irek.szczesniak@gmail.com>> >> >> 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, >> Irek >> >> -- >> Ireneusz (Irek) Szczesniak >> http://www.irkos.org >> _______________________________________________ >> Bridge mailing list >> Bridge@lists.linux-foundation.org >> <mailto:Bridge@lists.linux-foundation.org> >> https://lists.linux-foundation.org/mailman/listinfo/bridge >> > > > -- > Ireneusz (Irek) Szczesniak > http://www.irkos.org > _______________________________________________ > Bridge mailing list > Bridge@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/bridge > ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2011-04-25 20:43 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-04-25 9:37 [Bridge] mind-boggling questions Ireneusz Szcześniak 2011-04-25 11:02 ` Sasikanth V 2011-04-25 18:32 ` Ireneusz Szcześniak 2011-04-25 20:43 ` Joel Wiramu Pauling
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