[Bridge] How are MAC-addresses of the bridge-device computed?

Wayback MachineAbout this captureCOLLECTED BY Organization: Alexa Crawls Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period. Collection: Alexa Crawls DE Crawl data donated by Alexa Internet. This data is currently not publicly accessible TIMESTAMPSloadingLennert Buytenhekbuytenh@gnu.org
Mon, 31 Jan 2000 15:51:19 +0100 (MET)On Mon, 31 Jan 2000, Lars Bohn wrote:> Hi!Hello there!> For my systems-admin I need to know which Hardwareaddresses are used by the> bridge-device. The address seems to change every time I start the bridge up.The 802.1d spec recommends taking the lowest (when compared memcmp()-wise)MAC address, calculated over all of the interfaces. So if we have00:00:01:24:45:cf and 00:80:00:12:73:22 it’s going to be00:00:01:24:45:cf (see?)This makes sense (in the sense that it’s unique for a given bridge), butwe do not always know what MAC addresses are going to be enslaved when wecreate the bridge.I’ve ‘solved’ this by appending a 4-byte random number to the string FE:FF(or something), so yes, it changes every time.With the new snapshot, it should not matter, because the bridge should usethe interface MAC address for originating frames, so the internal bridgeaddress shouldn’t be visible (except when the bridge itself sends framesout of course).I will look into making things more ‘sane’ over the next couple of days.The major problem is that the bridge address might change if we take thelowest address, but if we don’t, then the bridge address depends on theorder in which we enslave the devices. Which is, in the general case, notacceptable.The address changing confuses things because the root bridge selectionalgorithm (in the STP) depends on being able to numerically compare MACaddresses. So the entire spanning tree might change due to enslaving of an(to the current topology unrelated) interface.Also, ARP might get confused.Greetings,Lennert

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