Security Basics mailing list archives
Re: TCP/IP CRC question
From: Don Parker <dparker () bridonsecurity com>
Date: Wed, 6 Oct 2004 10:46:38 -0700
Hi Jorge, the checksum is used for all four core protocls. It is also calculated by the sending computer. Each time it traverses a router it is then recalculated as the ttl value changes. Please bear in mind though that the checksum is only for the header itself. This checksum is there so that the destination computer once it receives the packet will recompute the checksum to confirm the packet was not corrupted from the last hop. Hopefully this answers your questions. Cheers, Don -------------------------------------------------------------- Don Parker, GCIA GCIH Intrusion Detection & Incident Handling Specialist Bridon Security & Training Services http://www.bridonsecurity.com voice: 1-613-302-2910 -------------------------------------------------------------- On Wed, 06 Oct 2004 01:15 , Jorge Mendez Bonini <jlmb () cableonda net> sent:
I've been reading about the TCP/IP protocol stack (TCP/Ilustrated Vol1 by Richard Stevens) lately and since Ethernet is quite common nowadays almost all link layer examples refer to it (I also checked Douglas Comer Internetworking with TCP/IP vol1). I tried searching RFC but found it very time consuming without good results (maybe I'm not used to it...yet) The Ethernet Frame contains a field known as FCS which contains a CRC. Now, my question is: If the CRC is generated from DATA field among others, What's the point of using checksums on the upper protocolos (IP checksums etc..)? Thanks for your time.
Current thread:
- Re: TCP/IP CRC question, (continued)
- Re: TCP/IP CRC question Jonathan Loh (Oct 07)
- RE: TCP/IP CRC question Shaineel Singh (Oct 07)
- Re: TCP/IP CRC question Alex V . Lukyanenko (Oct 07)
- Re: TCP/IP CRC question Fernando Gont (Oct 07)
- RE: TCP/IP CRC question Shaineel Singh (Oct 07)
- Re: TCP/IP CRC question Ansgar -59cobalt- Wiechers (Oct 07)
- Re: TCP/IP CRC question Fernando Gont (Oct 07)
- Re: TCP/IP CRC question Miles Stevenson (Oct 07)
- Re: TCP/IP CRC question Miles Stevenson (Oct 08)
- RE: TCP/IP CRC question Clement Dupuis (Oct 12)
- Re: TCP/IP CRC question Miles Stevenson (Oct 08)
- Re: TCP/IP CRC question Don Parker (Oct 07)
- RE: TCP/IP CRC question Ted A (Oct 07)
- RE: TCP/IP CRC question Simon Zuckerbraun (Oct 13)