Security Basics mailing list archives
Re: TCP/IP CRC question
From: Fernando Gont <fernando () gont com ar>
Date: Thu, 07 Oct 2004 15:27:00 -0300
At 02:11 07/10/2004 +0300, Alex V.Lukyanenko wrote:
JMB> The Ethernet Frame contains a field known as FCS which contains a CRC. JMB> Now, my question is: JMB> If the CRC is generated from DATA field among others, What's the point JMB> of using checksums on the upper protocolos (IP checksums etc..)? JMB> Thanks for your time. Because the protocols are independant of the underlying/overlying protocols, i.e.:
Not completely true: The TCP checksum is computed using a pseudoheader tha includes fields (the source and destination IP addresses) from the Internet Protocol (IP).
1. Ethernet can be used for the transmission of higher-level protocols that do not perform CRC checking
No. You still need end-to-end error detection. Google for "end-to-end arguments in system design"., a classic paper which includes stuff on this issue.
2. IP can go over a protocol that does not perform CRC checking.
True for IPv4, although not strictly true for IPv6. -- Fernando Gont e-mail: fernando () gont com ar || fgont () acm org
Current thread:
- TCP/IP CRC question Jorge Mendez Bonini (Oct 06)
- RE: TCP/IP CRC question David Gillett (Oct 07)
- 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)
- <Possible follow-ups>
- 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)