Re: Checksum at INIT ACK.

[Daniel Borkmann <daniel@iogearbox.net>]

On 05/13/2015 08:48 AM, Moohyoung KIM wrote:
> Thanks for your kind response
> 
> The root cause of this problem is probably lksctp that is included in Linux 2.6.32-432.
> I found the lksctp that is included in Linux 2.6.32-504 is changed something related to checksum.
> When using virtual IP on bonding interface as our configuration, old lksctp did not set checksum value into their header.
> 
> After installing kernel update that include new lksctp that this problem is patched, the checksum is successfully set.

I have no concrete overview on RHEL anymore, but I remember that there
was a bug when using SCTP over f.e. bonding which if I remember correctly
the commit below fixed (there are also some more recent ones doing the
same for xfrm):

commit b73c43f884b1b26ef8e824a33f3924f92e493c11
Author: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Date:   Wed Jul 13 14:10:29 2011 +0000

    net: sctp: fix checksum marking for outgoing packets

    Packets to devices without NETIF_F_SCTP_CSUM (including NETIF_F_NO_CSUM)
    should be properly checksummed because the packets can be diverted or
    rerouted after construction. This still leaves packets diverted from
    NETIF_F_SCTP_CSUM-enabled devices with broken checksums. Fixing this
    needs implementing software offload fallback in networking core.

    For users of sctp_checksum_disable, skb->ip_summed should be left as
    CHECKSUM_NONE and not CHECKSUM_UNNECESSARY as per include/linux/skbuff.h.

    Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
    Signed-off-by: David S. Miller <davem@davemloft.net>

That's why you most likely don't see this anymore on newer RHEL6.

> Thanks
> 
> 2015. 5. 13., 오후 2:55, Michael Tuexen <Michael.Tuexen@lurchi.franken.de> 작성:
> 
>> On 13 May 2015, at 04:14, Moohyoung KIM <emusal@gmail.com> wrote:
>>
>> Dear all,
>>
>> I am currently trying to make an association with otter vendor's system. but it is failed.
>> The engineer of peer side requests me to set checksum parameter into INIT Ack. message we sent.
>>
>> Q1. is it possible to differently set checksum value for each associations on linux-sctp?
>> Q2-1. If it is possible to set checksum separately, how to set the flag either use or not?
>> Q2-2. If it is NOT possible, we MUST turn the checksum feature on for whole association? how to do that? I am using lksctp-1.0.10-7 on Linux 2.6.32-432 (RHEL6).
> SCTP only uses CRC32c as the checksum and it is mandatory to use it. There is no
> "checksum parameter" for negotiating it.
> Does your peer still use the deprecated Adler32? It has been changed to CRC32c in
> https://tools.ietf.org/html/rfc3309
> The updated SCTP specification
> https://tools.ietf.org/html/rfc4960
> doesn't mention Adler32 anymore.
> 
> Best regards
> Michael

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