Ethereal-users: Re: [Ethereal-users] confusion about TCP checksum calculation

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From: Hamish Moffatt <hamish@xxxxxxxxxxxx>
Date: Wed, 2 Jan 2002 11:42:58 +1100
On Wed, Jan 02, 2002 at 09:03:59AM +1100, Ronnie Sahlberg wrote:
> TCP cheacksums are based on both the TCP layer as well as a IP pseudo
> header.
> The IP pseudo header contains some fileds as IP address and such.
> Please see RFC793
> 
> If you change some fields in the IP layer, then the TCP checksum will also
> be modified.

Thanks Ronnie. I'm aware that the TCP checksum includes some IP header
fields. However the IP has not changed and the IP header checksum
is still considered correct.

Oddly enough the IP header has the total length field set to 1500
(as captured), which is wrong.

Hamish
-- 
Hamish Moffatt VK3SB <hamish@xxxxxxxxxx> <hamish@xxxxxxxxxxxx>