Security Basics mailing list archives
Re: TCP/IP CRC question
From: Fernando Gont <fernando () gont com ar>
Date: Thu, 07 Oct 2004 15:20:59 -0300
At 01:15 06/10/2004 -0500, Jorge Mendez Bonini wrote:
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..)?
First, the link-layer checksum "protects" data only on agiven network segment.Also, some of the links in the path may not implement error detection. Therefore you need to implement this function yourself in upper layers. The IP checksum protects the IP header on a end-node to end-node basis. However, it does not protect the payload. The TCP checksum protects data on an end-to-end basis (strictly speaking, not really).
Finally, CRCs and checksums catch different type of errors. Checksums catch single bit errors (which usually happen at routers' memories), while CRCs protect data against burst error (continuous bits in the data stream are corrupted).
-- 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)