Re: RFC 1812, section 4.2.2.5
William Chops Westfield <billw@cisco.com> Sun, 17 September 1995 07:14 UTC
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From: William Chops Westfield <billw@cisco.com>
To: Craig Partridge <craig@aland.bbn.com>
Subject: Re: RFC 1812, section 4.2.2.5
In-Reply-To: Your message of Thu, 14 Sep 95 17:25:26 -0700
Cc: rreq@isi.edu
Message-Id: <CMM.0.90.2.811320314.billw@puli.cisco.com>
2. You can skip verifying the IP checksum if you use incremental checksum updating and the only field being changed is the ttl. I read various related documents and sections of 1812, and I think either interpretation is valid, though there are hints that interpretation (1) may have been intended. I'm obviously very interested in doing (2), because on a processor I'm looking at, it represents a 25% performance hit to actually compute and check the checksum on the header. I think what it amounts to is that most people agreed that (2) might be an interesting approach, but no vendor was ever gutsy enough to do it and risk the resultant semi-technical ridicule that might occur in the competitive marketplace. (You know salescritters - it'd be "Yeah, the cisco's almost as fast as we are, but they don't even check if the packet's valid before they forward it.") I find it difficult to believe a 25% performance hit considering the other sanity checks that probably have to be made, but then I've never counted cycles through our fastest single-processor path... BillW cisco
- RFC 1812, section 4.2.2.5 Craig Partridge
- Re: RFC 1812, section 4.2.2.5 Fred Baker
- Re: RFC 1812, section 4.2.2.5 Tony Li
- Re: RFC 1812, section 4.2.2.5 Fred Baker
- Re: RFC 1812, section 4.2.2.5 Frank Kastenholz
- Re: RFC 1812, section 4.2.2.5 Frank Kastenholz
- Re: RFC 1812, section 4.2.2.5 John Shriver
- Re: RFC 1812, section 4.2.2.5 Tony Li
- Re: RFC 1812, section 4.2.2.5 Noel Chiappa
- Re: RFC 1812, section 4.2.2.5 William Chops Westfield
- Re: RFC 1812, section 4.2.2.5 Tony Li
- Re: RFC 1812, section 4.2.2.5 braden