Date: Thu, 19 Feb 1998 15:59:02 +0200 From: Nadav Eiron <nadav@barcode.co.il> To: Norman C Rice <nrice@emu.sourcee.com> Cc: jgrosch@superior.mooseriver.com, questions@FreeBSD.ORG Subject: Re: hostid equals Ethernet address or IP address ? Message-ID: <34EC3AA6.562C@barcode.co.il> References: <19980219004112.26662@mooseriver.com> <19980219084843.13569@emu.sourcee.com>
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Norman C Rice wrote: > > On Thu, Feb 19, 1998 at 12:41:12AM -0800, Josef Grosch wrote: [snip] > > While I am not sure about supporting documents, I am pretty sure that > sethostid(3) is referring to the IP address, not the MAC address. My > reasoning is that IP addresses are 32-bits while MAC address are > 64-bits (the first 32-bits comprises the OUI which uniquely identifies > the vendor). My other thought is that if sethostid() actually rewrote > the MAC address (assuming it was implemented in FLASH, EEPROM, or some > other reprogrammable device) is that there would be no guarantee of > uniqueness. Reprogramming the MAC address would ``break'' many vendors > cards due to the steps they take to prevent this, e.g., embedded > CRC-32s, checksums, inverted MAC addresses, etc.. As stated in the man page, the function is deprecated anyhow, but just to comment on Norman Rice's answer: MAC addresses are 48 bit long, not 64 bit long, and there are indeed cases where they are reprogrammed. The most notable of these is DECnet Phase IV where the MAC address is reprogrammed to be the DECnet address (with some additions) as soon as DECnet is up and running. Most NICs will let you reprogram their MAC address temporarily, if you so wish. > > > > > > > Josef > > > > -- > > Josef Grosch | Another day closer to a | FreeBSD 2.2.5 > > jgrosch@MooseRiver.com | Micro$oft free world | UNIX for the masses > -- > Regards, > Norman C. Rice, Jr. Nadav To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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