Date: Thu, 26 Mar 1998 15:45:59 -0500 (EST) From: <david@sparks.net> To: "Ron G. Minnich" <rminnich@Sarnoff.COM> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: ARP REQUEST question Message-ID: <Pine.BSI.3.95.980326154320.8002D-100000@sparks.net> In-Reply-To: <Pine.SUN.3.91.980325151635.9569E-100000@terra>
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On Wed, 25 Mar 1998, Ron G. Minnich wrote: > On Wed, 25 Mar 1998, David Greenman wrote: > > Switches should be checking the CRC on inbound packets and discarding > > them if it is bad, so I don't see a problem. > > No problem if the crc on the inbound packet is bad. Discard it. Suppose > there's a problem though between the 'inbound crc check' and the 'outbound > crc generate' such that one bit in the packet is corrupted. Say, a pattern > that results in a marginal component internal to the switch corrupting > data, then the corrupt data is used to generate crc-32 on the outgoing > side. Boom, corrupted packet, no indication. This can and does happen. > > Checksums have to be end-to-end. What meaning does an arp entry have for an interface which is not on a local interface? And if it *is* on a local interface, the level two error checking should handle it. > Most recent (humorous) example: Don Becker reports that he detected > problems with gigabit ethernet cards via IP checksums. The problems > occured (yikes!) on the destination machine, as the data was transferred > from the card to main memory. No crc-32 error can catch that one, since > it's already been checked on the card. Ouch. Uhmm, using software to determine whether the hardware which is running on it is functioning properly sounds generally self-defeating. --- David ---------------------------------------------------------------------------- It's *amazing* what one can accomplish when one doesn't know what one can't do! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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