Re: [PATCH net-next v4 4/4] selftests/net: packetdrill: add TCP MTU probing test

[Neal Cardwell]

On Tue, Nov 10, 2026 at 11:46 AM Yongjian Wang via B4 Relay
<devnull+echoowall.gmail.com@xxxxxxxxxx> wrote:
>
> From: Yongjian Wang <echoowall@xxxxxxxxx>
>
> Packetization layer path MTU discovery (net.ipv4.tcp_mtu_probing=2) has
> no selftest coverage.
>
> Add a test for an active connection. Check that it starts at
> tcp_base_mss, that it sends the first probe half way between
> tcp_base_mss and the peer's MSS once cwnd allows it, and that an
> acknowledged probe raises the MSS and leads to a larger probe.
>
> The SYN offers timestamps and the scripted SYN-ACK declines them.
> This also checks that MTU probing uses the negotiated header length
> for the initial send MSS.
>
> Signed-off-by: Yongjian Wang <echoowall@xxxxxxxxx>
> ---

Reviewed-by: Neal Cardwell <ncardwell@xxxxxxxxxx>

Thanks!
neal