From: Mat Martineau <mathew.j.martineau@linux.intel.com>
To: Paolo Abeni <pabeni@redhat.com>
Cc: Matthieu Baerts <matthieu.baerts@tessares.net>,
Geliang Tang <geliangtang@gmail.com>,
mptcp@lists.linux.dev
Subject: Re: MPTCP checksum interop
Date: Mon, 14 Jun 2021 17:14:29 -0700 (PDT) [thread overview]
Message-ID: <be45ce3-c6ab-df89-96cc-1f9cdb4babdc@linux.intel.com> (raw)
In-Reply-To: <8cceb711ad974911da62d62a354e6569b573e0b2.camel@redhat.com>
On Mon, 14 Jun 2021, Paolo Abeni wrote:
> Hello
>
> On Fri, 2021-06-11 at 20:57 -0700, Mat Martineau wrote:
>> I did some tests with connections with checksums enabled, between the
>> export branch and the multipath-tcp.org mptcp_trunk branch (v1 mode).
>
> Thank you for checking!
>
>> When the multipath-tcp.org kernel was listening, the connection would
>> always fall back to TCP when the first data was sent by the upstream
>> kernel. The multipath-tcp.org kernel was the first to fall back and stop
>> sending MPTCP headers.
>
> This sounds like a csum error detected ??! What does wireshark say
> about the MPTCP csum value?
Wireshark doesn't complain about the checksum, and the MPTCP option parses
cleanly.
Fallback appears to have more to do with mptcp_trunk's handling for
MP_CAPABLE + data. I turned on debug output on the mptcp_trunk side and
saw:
mptcp_prevalidate_skb: mptcp_prevalidate_skb 0xc20cfa4 will fallback - pi 1 from tcp_data_queue+0x444/0x600, seq 2884338481 mptcp-flags 0x0
This might be the problem in mptcp.h:
#define MPTCPV1_SUB_LEN_CAPABLE_DATA 22
#define MPTCPV1_SUB_LEN_CAPABLE_DATA_CSUM 22 // <---- should be 24
>
>> When the upstream kernel was listening, the multipath-tcp.org kernel would
>> send corrupt TCP options with the first data packet (the first time a DSS
>> option was sent). The upstream kernel would then send TCP RST.
>
> How does TCP option look like? Could you please share a short pcap
> snippet?
The MPTCP option is not of the correct length to contain a checksum, and
the bytes after the MPTCP option are getting interpreted by Wireshark as a
separate (broken) option. That broken option looks like random bytes:
invalid option number and way-too-large option length. The
multipath-tcp.org kernel is also sending MP_CAPABLE + data here. The above
definitions look suspicous for this too.
I'll add a github issue and upload the .pcap
--
Mat Martineau
Intel
prev parent reply other threads:[~2021-06-15 0:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-12 3:57 MPTCP checksum interop Mat Martineau
2021-06-14 8:30 ` Paolo Abeni
2021-06-15 0:14 ` Mat Martineau [this message]
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