Date: Mon, 27 Aug 2001 10:18:07 -0700 From: Justin C.Walker <justin@mac.com> To: freebsd-mobile@FreeBSD.ORG Subject: Re: Frustrating network problem - need diagnotic help Message-ID: <20010827171808.LXNV29510.femail39.sdc1.sfba.home.com@grinch> In-Reply-To: <200108271707.f7RH73R23446@ptavv.es.net>
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On Monday, August 27, 2001, at 10:07 AM, Kevin Oberman wrote: >> From: "Chad R. Larson" <chad@freebie.dcfinc.com> >> Date: Mon, 27 Aug 101 09:29:34 -0700 (MST) >> Sender: chad@freebie.dcfinc.com >> >>>> "Kevin Oberman" <oberman@es.net> writes: >>> If you tweak the software to assign a MAC address to the something >>> else that is locally administered (different from setting the MAC to >>> the globally unique address of some older interface that failed), the >>> hex would be: a:0:2b:3f:a5:15 (not that anyone does this any longer >>> and there is no reason to assume that any part of the hardware MAC >>> would be used if you are using a locally administered MAC). >> >> Actually, once you've set the second bit (mask 0x04), the other >> 46 bits >> can be anything you want them to be =and= you assume the >> responsibility >> for assuring they are unique within your collision domain. >> >> And, I don't recall a rule that says you can't have a multicast >> source address (though my 802.3 book is at the office). So, I'd >> agree that the source address he's reporting is most probably >> borked, but if that first byte were 0x03 (vs 0x01) he'd probably be >> legal. But that's also probably not what he wants... > > Chad, > > I'm afraid not. I do have my 802.3 handy and the source address field > is not interpreted at all. To be pedantic, (my copy of) the spec sez that bit 0 of the source is wired to zero. You can figure that any way you want, but the implication is that you can't send a frame with the 'group address' bit set from a conforming transmitter. To be even more pedantic, isn't "the second bit" mask 0x2 (from the preceding poster)? > The I/G bit (individual/group) bit is > ALWAYS interpreted in a destination address, so setting the "locally > admin" bit does not over-ride this functionality. The import is that > many devices (including switches) make forwarding decisions based on > the setting of this bit. > > In any case, a hardware MAC address that has the group address bit set > is clearly broken. Amen. Regards, Justin --- Justin C. Walker, Curmudgeon-At-Large * Institute for General Semantics | Director of Technology | If you're not confused, Nexsi Systems Corp. | You're not paying attention 1959 Concourse Drive | San Jose, CA 95131 | *--------------------------------------*-------------------------------* To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message
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