Subject: Re: UDP checksum trouble in -current
To: None <email@example.com>
From: YAMAMOTO Takashi <firstname.lastname@example.org>
Date: 01/22/2005 19:49:52
> If the receiver is the kernel it is not a problem, but if the receiver is
> a BPF or raw socket it can be.
can raw sockets receive udp packets?
> Either of those may attempt to check the
> UDP ckecksum (tcpdump does, for example). 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.
ok, i see your point. thanks for explanation.
however, i disagree.
- tcpdump/bpf is also used when debugging network stack.
in that case, seeing garbage as-is is even expected.
- if you really care about "correctness" of tapped packets,
you should put correct sums. zero is not really correct, even for udp.
i guess we decided not to care about this kind of "correctness" much
when we decided to do checksum offloading/omission.