On 11/10/22 13:29, Morten Brørup wrote:
From: Andrew Rybchenko [mailto:andrew.rybche...@oktetlabs.ru]
Sent: Thursday, 10 November 2022 11.09
On 11/10/22 12:55, Morten Brørup wrote:
From: Andrew Rybchenko [mailto:andrew.rybche...@oktetlabs.ru]
Sent: Thursday, 10 November 2022 10.26
Hi all,
some drivers report RTE_MBUF_F_RX_IP_CKSUM_GOOD for IPv6 packets.
For me it looks strange, but I see some technical reasons behind.
Please note: IPv6 packets by definition have no IP checksum.
Documentation in lib/mbuf/rte_mbuf_core.h is a bit vague.
Should UNKNOWN or NONE be used instead?
Certainly not NONE. Its description says: "the IP checksum is *not*
correct in the packet [...]". But there is no incorrect IP checksum in
the packet.
Thanks, I should read the definition of none more careful.
I will argue against UNKNOWN. Its description says: "no information
about the RX IP checksum". But we do have information about it! We know
that the IP checksum is not there (the value is "NULL"), and that it is
not supposed to be there (the value is supposed to be "NULL").
I thought that "no checksum" => "no information" => UNKNOWN
That was my initial interpretation too, and it stuck with me for a while.
But then I tried hard to read it differently, tweaking it to support the
conclusion I was looking for.
So I consider GOOD the correct response here.
GOOD also means that the application can proceed processing the
packet normally without further IP header checksum checking, so it's
good for performance.
It is very important point and would be nice to have in GOOD
case definition (both IP and L4 cases). It is the right
motivation why GOOD makes sense for IPv6.
It should be added to the description of RTE_MBUF_F_RX_IP_CKSUM_GOOD
that IPv6 packets always return this value, because IPv6 packets have
no IP header checksum, and that is what is expected of them.
Could you make a patch?
Too busy right now, but I'll put it on my todo list. :-)
Bonus question is UDP checksum 0 case. GOOD as well?
(just want to clarify the documentation while we're on it).
No. The UDP checksum is not optional in IPv6.
RFC 2460 section 8.1 bullet 4 says: "Unlike IPv4, when UDP packets are originated by
an IPv6 node, the UDP checksum is not optional. [...] IPv6 receivers must discard UDP
packets containing a zero checksum, and should log the error."
Yes I know, but I'm asking about IPv4 case with UDP checksum 0.
