On Mon, 23 Jan 2006 22:48:23 -0800 "Ashley Hatch" <spam@xxxxxxxxxxxx> wrote: > - SUMMARY - > > It seems like you should be able to assign your MAC on the bridging > interfaces for IP L2 -> L3 mappings, or at least choose which NIC > supplies the MAC. > > Since my L2 mapping to my L3 address has nothing to do with my STP > bridge ID, why can't we decouple them and have MAC locking or setting > as an option to BRCTL and the kernel module so that brctl could > prefer a NIC or ifconfig could set it for the purposes of IP? > > - END SUMMARY - > > Presently the system choose the lowest MAC for the purposes of STP > and also assigns this MAC for the purposes of IP. This is fine for > STP but certainly unnecessary for IP. The bridge ID and the IP/MAC do > not need to be the same and in some cases certainly should not be > (unless I'm missing something obvious). > > I have looked through the code of brctl and the ethernet bridging > code in the kernel and I have not found a way to resolve the > following issue short of recoding it, and I can't seem to get a > google search to help either. > > When I create a bridging interface doing something like this: > > brctl addbr br0 > brctl addif br0 eth0 > brctl addif br0 eth1 > > The resulting MAC address of the interface br0 is the lowest of all > MACs. From an STP standpoint, this makes sense. I am using VMWARE > virtual interfaces on a few machines, and these MACs are lower than > some of my real NICs. They are not unique however. So when I bridge > my virtual net and vmnet I sometimes get non-unique MACs on my real > L2 network and the machines with the non-unique MAC of course cannot > communicate. What I am doing to get around this is assign my REAL NIC > MACs from OUIs which make them lower than the vmnet OUI. That feels > tacky and wrong. > > I thought to myself, "I'll just assign BR0 the MAC of my NIC (which > is higher than VMNET2)." Alas > > ifconfig br0 hw ether aa:bb:cc:dd:ee:ff > > Gives an ioctl error, and indeed is insupported in the kernel as far > as I can tell. A buddy of mine and I are trying to hack it in, but it > seems like something that should be in the mainline of the kernel. > > If noone in briding is willing to support it, will someone consider a > patch to do it? > > Thanks, > Ashley Hatch > Senior Network Engineer - UNLV In 2.6.15 or later it can be changed to any of the existing interfaces. I allowed that because it won't break the forwarding tables, and only slightly effects STP. (There is a higher risk of STP cycles). -- Stephen Hemminger <shemminger@xxxxxxxx> OSDL http://developer.osdl.org/~shemminger
