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Date: Tue, 27 Apr 2004 22:05:43 +0300
From: Ruslan Ermilov <ru@freebsd.org>
To: Mark Santcroos <marks@ripe.net>
Message-ID: <20040427190543.GA75827@ip.net.ua>
References: <20040427160901.GA2552@laptop.6bone.nl>
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cc: net@freebsd.org
Subject: Re: udp checksum on raw sockets
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On Tue, Apr 27, 2004 at 06:09:01PM +0200, Mark Santcroos wrote:
> * I'm sending UDP packets on a raw socket.
>=20
> * iphdr->ip_src.s_addr =3D INADDR_ANY;
>   So I don't know the IP address that will be used as src address.
>   So as far as I can see, I have a problem generating the checksum in
>   userspace.
>=20
Yes, that problem is real.

> Suggestion:
>=20
> Would it make sense that if:
> sysctl net.udp.checksum=3D1
> and
> udphdr->uh_sum =3D 0;
> in a UDP packet created on a raw socket, to do the checksum in the kernel
> instead of leaving it zero? If it does, I can create a patch.
>=20
> Any other hints as how to do the checksum in userland are welcome too. As
> that is the "ultimate" problem I try to fix.
>=20
Have the raw IP code set csum_flags |=3D CSUM_UDP (and set csum_data
correctly) in m->m_pkthdr, if ip_p =3D=3D IPPROTO_UDP && uh_csum =3D=3D 0.
Do the same thing for IPPROTO_TCP.


Cheers,
--=20
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer

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