Re: [PATCH net-next v2 06/15] mptcp: pm: drop TCP TS with ADD_ADDRv6 + port

[Matthieu Baerts]

Hello,

On 05/06/2026 19:21, Matthieu Baerts (NGI0) wrote:
> With TCP-timestamps (padded) taking 12 bytes and ADD_ADDR IPv6 + port
> taking 30 bytes, the 40-byte limit for the TCP options is reached. In
> this case, it is then not possible to send the signal.
> 
> To be able to send this ADD_ADDR, the TCP timestamps option can now be
> dropped. This is done, when needed by setting the *drop_ts parameter
> from mptcp_established_options. This feature is controlled by a new
> net.mptcp.add_addr_v6_port_drop_ts sysctl knob, enabled by default.
> 
> It is important to keep in mind that dropping the TCP timestamps option
> for one packet of the connection could eventually disrupt some
> middleboxes: even if it should be unlikely, they could drop the packet
> or even block the connection. That's why this new feature can be
> controlled by a sysctl knob.
FYI, Sashiko's new comments about this patch [1] are suggesting issues
when MPTCP is used in parallel with TCP MD5. But MPTCP cannot be used
with MD5 because there is not enough space in the TCP options. That's
why there is an explicit rejection when initiating the connection.

So I think we can ignore these comments saying that more options could
be dropped, and the size can be negative.

https://sashiko.dev/#/patchset/20260605-net-next-mptcp-add-addr6-port-ts-v2-0-758e7ca73f4d%40kernel.org?part=6

Cheers,
Matt
-- 
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