Date: Wed, 29 Oct 1997 17:49:28 -0500 (EST) From: "David E. Cross" <dec@phoenix.its.rpi.edu> To: Jonathan Lemon <jlemon@americantv.com> Cc: Sunthiti Patchararungruang <stt@pluto.cpe.ku.ac.th>, freebsd-hackers@FreeBSD.ORG Subject: Re: Kernel modification Message-ID: <Pine.BSF.3.96.971029174626.16229D-100000@phoenix.its.rpi.edu> In-Reply-To: <19971029161422.12013@right.PCS>
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On Wed, 29 Oct 1997, Jonathan Lemon wrote: > > program on FreeBSD2.2.2. It need to copy a data link frame from an > > interface to another one. The data frame must not be changed even in > > ethernet address field. I use BPF. I have found that the system always > > change my ethernet source address to the address of the output interface. > > AFAIK, this is correct. I believe that the Ethernet specification > requires that the source MAC address in the ethernet frame correspond > to the hardware address of the transmitting device. > > I can't see why you would want to re-transmit with the original MAC > address; this would cause arp lookups to fail, among other things. > > Even bridges put their own MAC address in the frame. > The ether switches that we have here keep the orignial source frame. In my understanding of the INTENT of MAC addresses, it would make more sense for bridges, switches to keep the original source address, else it would have to broadcast (or at least multicast) the responce on the other side of the interface (how would it know which MAC address the packet wsa 'really' destined for? -- David Cros ACS Consultant
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