Subject: Re: UDP checksum trouble in -current
To: William Allen Simpson <email@example.com>
From: Steven M. Bellovin <firstname.lastname@example.org>
Date: 01/21/2005 18:52:55
In message <41F18074.email@example.com>, William Allen Simpson writes:
>john heasley wrote:
>>A value of zero is a clear
>>indication not to check it for UDP. It seems like little pain to be
>>I do not know what could be done for IP or TCP checksums. But, if I'm not
>>mistaken, zero is not a valid value for either and might be a good indicator
>>that no checksumming was performed.
>Both IP and TCP checksums MUST be performed.
>Zero is not a valid value for UDP, and indicates no checksum. The field
>still must be set to something. Don't leave uninitialized fields.
You can use a zero checksum for IPv4 UDP, but not for IPv6, I believe.
--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb