Date: Tue, 12 Oct 1999 18:33:49 +0200 From: Wim Livens <livensw@rc.bel.alcatel.be> To: freebsd-net@freebsd.org Subject: Why copying data is needed for forwarding IP packets ? Message-ID: <19991012183349.D7794@rc.bel.alcatel.be>
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In Stevens' volume II book, the following is mentioned: "Two operations dominate the time required to process packets: copying data end computing checksums." (section 8.7, p. 234). What is meant exactly by copying data here ? Am I correct in saying that to forward a packet received on one interface and send it out on another interface, the packet is stored in host memory by the first interface card, then some fields are modified, and then the second interface card reads the packet from host memory and send it out on the wire (maybe using some buffering on the card) ? Or is the data copied from host memory to host memory somewhere ? Does the same hold for multicast ? Thanks for any clarification, -- Wim Livens. Alcatel - Corporate Research Center wim.livens@alcatel.be Fr. Wellesplein 1 livensw@rc.bel.alcatel.be B-2018 Antwerpen Tel: +32 3 240 7570 Belgium. Fax: +32 3 240 9932 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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