Date: Mon, 27 Aug 2001 10:07:03 -0700 From: "Kevin Oberman" <oberman@es.net> To: chad@dcfinc.com Cc: reader@newsguy.com, freebsd-mobile@FreeBSD.ORG Subject: Re: Frustrating network problem - need diagnotic help Message-ID: <200108271707.f7RH73R23446@ptavv.es.net> In-Reply-To: Your message of "Mon, 27 Aug 2001 09:29:34 PDT." <200108271633.JAA18022@freebie.dcfinc.com>
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> 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. 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. R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message
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