[PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Eric Dumazet]

This test checks syncookie mode is able to reconstruct some
client options when TCP TS are used:

- wscale option.
- sackOK.
- MSS (in a limited way).
- ECN (not tested, because of limited value).

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 .../net/packetdrill/tcp_syncookies_ip6_9k.pkt | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt

diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
new file mode 100644
index 0000000000000000000000000000000000000000..15d03992a99140ecc4241edae58693dc5098fece
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Check syncookies.
+//
+// Check we are able to rebuild client sack, wscale and mss options.
+// IPv6 msstab[4] = { 1280 - 60, 1480 - 60, 1500 - 60, 9000 - 60 }
+
+--ip_version=ipv6
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip link set dev tun0 mtu 9000
+`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 32792 <mss 8940,sackOK,TS val 100 ecr 0,nop,wscale 10>
+   +0 > S. 0:0(0) ack 1 <mss 8940,sackOK,TS val 4000 ecr 100,nop,wscale 8>
+ +.01 < . 1:1(0) ack 1 win 1024 <nop,nop,TS val 110 ecr 4000>
+
+   +0 accept(3, ..., ...) = 4
+
+// Check we properly infer from the final packet the other peer wanted 8940 mss, wscale 10 and sackOK
+   +0 %{ assert tcpi_snd_mss == 8928, tcpi_snd_mss }%
+   +0 %{ assert tcpi_snd_wscale = 10, tcpi_snd_wscale }%
+   +0 %{ assert (tcpi_options & TCPI_OPT_WSCALE) != 0, tcpi_options }%
+
-- 
2.54.0.545.g6539524ca2-goog

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Neal Cardwell]

On Wed, Apr 29, 2026 at 4:00 AM Eric Dumazet <edumazet@google.com> wrote:
>
> This test checks syncookie mode is able to reconstruct some
> client options when TCP TS are used:
>
> - wscale option.
> - sackOK.
> - MSS (in a limited way).
> - ECN (not tested, because of limited value).
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  .../net/packetdrill/tcp_syncookies_ip6_9k.pkt | 30 +++++++++++++++++++
>  1 file changed, 30 insertions(+)
>  create mode 100644 tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
>
> diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
> new file mode 100644
> index 0000000000000000000000000000000000000000..15d03992a99140ecc4241edae58693dc5098fece
> --- /dev/null
> +++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// Check syncookies.
> +//
> +// Check we are able to rebuild client sack, wscale and mss options.
> +// IPv6 msstab[4] = { 1280 - 60, 1480 - 60, 1500 - 60, 9000 - 60 }
> +
> +--ip_version=ipv6
> +
> +`./defaults.sh
> +sysctl -q net.ipv4.tcp_syncookies=2
> +ip link set dev tun0 mtu 9000
> +`
> +
> +    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> +   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> +   +0 bind(3, ..., ...) = 0
> +   +0 listen(3, 10) = 0
> +
> +   +0 < S 0:0(0) win 32792 <mss 8940,sackOK,TS val 100 ecr 0,nop,wscale 10>
> +   +0 > S. 0:0(0) ack 1 <mss 8940,sackOK,TS val 4000 ecr 100,nop,wscale 8>
> + +.01 < . 1:1(0) ack 1 win 1024 <nop,nop,TS val 110 ecr 4000>
> +
> +   +0 accept(3, ..., ...) = 4
> +
> +// Check we properly infer from the final packet the other peer wanted 8940 mss, wscale 10 and sackOK
> +   +0 %{ assert tcpi_snd_mss == 8928, tcpi_snd_mss }%
> +   +0 %{ assert tcpi_snd_wscale = 10, tcpi_snd_wscale }%
> +   +0 %{ assert (tcpi_options & TCPI_OPT_WSCALE) != 0, tcpi_options }%

The comment mentions checking sackOK but the script does not seem to
do that? Probably want to check the TCPI_OPT_SACK bit as well? Maybe
TCPI_OPT_TIMESTAMPS as well, for completeness?

Thanks for the test!

neal

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Eric Dumazet]

On Wed, Apr 29, 2026 at 7:15 AM Neal Cardwell <ncardwell@google.com> wrote:
>
> On Wed, Apr 29, 2026 at 4:00 AM Eric Dumazet <edumazet@google.com> wrote:
> >
> > This test checks syncookie mode is able to reconstruct some
> > client options when TCP TS are used:
> >
> > - wscale option.
> > - sackOK.
> > - MSS (in a limited way).
> > - ECN (not tested, because of limited value).
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > ---
> >  .../net/packetdrill/tcp_syncookies_ip6_9k.pkt | 30 +++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >  create mode 100644 tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
> >
> > diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..15d03992a99140ecc4241edae58693dc5098fece
> > --- /dev/null
> > +++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_ip6_9k.pkt
> > @@ -0,0 +1,30 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +//
> > +// Check syncookies.
> > +//
> > +// Check we are able to rebuild client sack, wscale and mss options.
> > +// IPv6 msstab[4] = { 1280 - 60, 1480 - 60, 1500 - 60, 9000 - 60 }
> > +
> > +--ip_version=ipv6
> > +
> > +`./defaults.sh
> > +sysctl -q net.ipv4.tcp_syncookies=2
> > +ip link set dev tun0 mtu 9000
> > +`
> > +
> > +    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> > +   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > +   +0 bind(3, ..., ...) = 0
> > +   +0 listen(3, 10) = 0
> > +
> > +   +0 < S 0:0(0) win 32792 <mss 8940,sackOK,TS val 100 ecr 0,nop,wscale 10>
> > +   +0 > S. 0:0(0) ack 1 <mss 8940,sackOK,TS val 4000 ecr 100,nop,wscale 8>
> > + +.01 < . 1:1(0) ack 1 win 1024 <nop,nop,TS val 110 ecr 4000>
> > +
> > +   +0 accept(3, ..., ...) = 4
> > +
> > +// Check we properly infer from the final packet the other peer wanted 8940 mss, wscale 10 and sackOK
> > +   +0 %{ assert tcpi_snd_mss == 8928, tcpi_snd_mss }%
> > +   +0 %{ assert tcpi_snd_wscale = 10, tcpi_snd_wscale }%
> > +   +0 %{ assert (tcpi_options & TCPI_OPT_WSCALE) != 0, tcpi_options }%
>
> The comment mentions checking sackOK but the script does not seem to
> do that? Probably want to check the TCPI_OPT_SACK bit as well? Maybe
> TCPI_OPT_TIMESTAMPS as well, for completeness?


Oh right, last minute typo, I was testing (tcpi_options & 2) != 0,
then wanted to replace with the symbolic version, which should have
been TCPI_OPT_SACK.

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Jakub Kicinski]

On Wed, 29 Apr 2026 08:00:36 +0000 Eric Dumazet wrote:
> This test checks syncookie mode is able to reconstruct some
> client options when TCP TS are used:
> 
> - wscale option.
> - sackOK.
> - MSS (in a limited way).
> - ECN (not tested, because of limited value).

We're getting:

# TAP version 13
# 1..1
#   File "/tmp/code_oyWax9", line 223
#     assert tcpi_snd_wscale = 10, tcpi_snd_wscale
#                            ^
# SyntaxError: invalid syntax
# tcp_syncookies_ip6_9k.pkt: error executing code: 'python3' returned non-zero status 1

do we need to update packetdrill ?

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Eric Dumazet]

On Wed, Apr 29, 2026 at 9:48 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 29 Apr 2026 08:00:36 +0000 Eric Dumazet wrote:
> > This test checks syncookie mode is able to reconstruct some
> > client options when TCP TS are used:
> >
> > - wscale option.
> > - sackOK.
> > - MSS (in a limited way).
> > - ECN (not tested, because of limited value).
>
> We're getting:
>
> # TAP version 13
> # 1..1
> #   File "/tmp/code_oyWax9", line 223
> #     assert tcpi_snd_wscale = 10, tcpi_snd_wscale
> #                            ^
> # SyntaxError: invalid syntax
> # tcp_syncookies_ip6_9k.pkt: error executing code: 'python3' returned non-zero status 1
>
> do we need to update packetdrill ?

No, this should have been

 assert tcpi_snd_wscale == 10, tcpi_snd_wscale

I initially had a value of 8, and decided going to 10 just to make it
different than the output wscale value.

Sorry for the confusion.

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Eric Dumazet]

On Wed, Apr 29, 2026 at 10:09 AM Eric Dumazet <edumazet@google.com> wrote:
>
> On Wed, Apr 29, 2026 at 9:48 AM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > On Wed, 29 Apr 2026 08:00:36 +0000 Eric Dumazet wrote:
> > > This test checks syncookie mode is able to reconstruct some
> > > client options when TCP TS are used:
> > >
> > > - wscale option.
> > > - sackOK.
> > > - MSS (in a limited way).
> > > - ECN (not tested, because of limited value).
> >
> > We're getting:
> >
> > # TAP version 13
> > # 1..1
> > #   File "/tmp/code_oyWax9", line 223
> > #     assert tcpi_snd_wscale = 10, tcpi_snd_wscale
> > #                            ^
> > # SyntaxError: invalid syntax
> > # tcp_syncookies_ip6_9k.pkt: error executing code: 'python3' returned non-zero status 1
> >
> > do we need to update packetdrill ?
>
> No, this should have been
>
>  assert tcpi_snd_wscale == 10, tcpi_snd_wscale
>
> I initially had a value of 8, and decided going to 10 just to make it
> different than the output wscale value.
>
> Sorry for the confusion.

Neal, can you take care of adding TCPI_OPT_SACK to packetdrill ?

Thanks!

diff --git a/gtests/net/packetdrill/code.c b/gtests/net/packetdrill/code.c
index d90bffabcfe6..6d8d20e64d8c 100644
--- a/gtests/net/packetdrill/code.c
+++ b/gtests/net/packetdrill/code.c
@@ -129,6 +129,7 @@ static void write_symbols(struct code_state *code)
        emit_var(code, "TCPI_OPT_WSCALE",       TCPI_OPT_WSCALE);
        emit_var(code, "TCPI_OPT_ECN",          TCPI_OPT_ECN);
        emit_var(code, "TCPI_OPT_SYN_DATA",     TCPI_OPT_SYN_DATA);
+       emit_var(code, "TCPI_OPT_SACK", TCPI_OPT_SACK);
 #endif  /* linux */
 }

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Neal Cardwell]

On Wed, Apr 29, 2026 at 1:15 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Wed, Apr 29, 2026 at 10:09 AM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Wed, Apr 29, 2026 at 9:48 AM Jakub Kicinski <kuba@kernel.org> wrote:
> > >
> > > On Wed, 29 Apr 2026 08:00:36 +0000 Eric Dumazet wrote:
> > > > This test checks syncookie mode is able to reconstruct some
> > > > client options when TCP TS are used:
> > > >
> > > > - wscale option.
> > > > - sackOK.
> > > > - MSS (in a limited way).
> > > > - ECN (not tested, because of limited value).
> > >
> > > We're getting:
> > >
> > > # TAP version 13
> > > # 1..1
> > > #   File "/tmp/code_oyWax9", line 223
> > > #     assert tcpi_snd_wscale = 10, tcpi_snd_wscale
> > > #                            ^
> > > # SyntaxError: invalid syntax
> > > # tcp_syncookies_ip6_9k.pkt: error executing code: 'python3' returned non-zero status 1
> > >
> > > do we need to update packetdrill ?
> >
> > No, this should have been
> >
> >  assert tcpi_snd_wscale == 10, tcpi_snd_wscale
> >
> > I initially had a value of 8, and decided going to 10 just to make it
> > different than the output wscale value.
> >
> > Sorry for the confusion.
>
> Neal, can you take care of adding TCPI_OPT_SACK to packetdrill ?
>
> Thanks!
>
> diff --git a/gtests/net/packetdrill/code.c b/gtests/net/packetdrill/code.c
> index d90bffabcfe6..6d8d20e64d8c 100644
> --- a/gtests/net/packetdrill/code.c
> +++ b/gtests/net/packetdrill/code.c
> @@ -129,6 +129,7 @@ static void write_symbols(struct code_state *code)
>         emit_var(code, "TCPI_OPT_WSCALE",       TCPI_OPT_WSCALE);
>         emit_var(code, "TCPI_OPT_ECN",          TCPI_OPT_ECN);
>         emit_var(code, "TCPI_OPT_SYN_DATA",     TCPI_OPT_SYN_DATA);
> +       emit_var(code, "TCPI_OPT_SACK", TCPI_OPT_SACK);
>  #endif  /* linux */
>  }

Sure! Done. I added all the missing bit values in the following commit:

https://github.com/google/packetdrill/commit/faa0dfb54065118625e169d3111ce09c65b20229

This can be picked up with the following, or similar:

  git clone https://github.com/google/packetdrill.git

neal

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Jakub Kicinski]

On Wed, 29 Apr 2026 16:47:14 -0400 Neal Cardwell wrote:
> > diff --git a/gtests/net/packetdrill/code.c b/gtests/net/packetdrill/code.c
> > index d90bffabcfe6..6d8d20e64d8c 100644
> > --- a/gtests/net/packetdrill/code.c
> > +++ b/gtests/net/packetdrill/code.c
> > @@ -129,6 +129,7 @@ static void write_symbols(struct code_state *code)
> >         emit_var(code, "TCPI_OPT_WSCALE",       TCPI_OPT_WSCALE);
> >         emit_var(code, "TCPI_OPT_ECN",          TCPI_OPT_ECN);
> >         emit_var(code, "TCPI_OPT_SYN_DATA",     TCPI_OPT_SYN_DATA);
> > +       emit_var(code, "TCPI_OPT_SACK", TCPI_OPT_SACK);
> >  #endif  /* linux */
> >  }  
> 
> Sure! Done. I added all the missing bit values in the following commit:
> 
> https://github.com/google/packetdrill/commit/faa0dfb54065118625e169d3111ce09c65b20229
> 
> This can be picked up with the following, or similar:
> 
>   git clone https://github.com/google/packetdrill.git

Updated in netdev CI.

Re: [PATCH net-next] selftests/net: packetdrill: add tcp_syncookies_ip6_9k

[Eric Dumazet]

On Wed, Apr 29, 2026 at 4:33 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 29 Apr 2026 16:47:14 -0400 Neal Cardwell wrote:
> > > diff --git a/gtests/net/packetdrill/code.c b/gtests/net/packetdrill/code.c
> > > index d90bffabcfe6..6d8d20e64d8c 100644
> > > --- a/gtests/net/packetdrill/code.c
> > > +++ b/gtests/net/packetdrill/code.c
> > > @@ -129,6 +129,7 @@ static void write_symbols(struct code_state *code)
> > >         emit_var(code, "TCPI_OPT_WSCALE",       TCPI_OPT_WSCALE);
> > >         emit_var(code, "TCPI_OPT_ECN",          TCPI_OPT_ECN);
> > >         emit_var(code, "TCPI_OPT_SYN_DATA",     TCPI_OPT_SYN_DATA);
> > > +       emit_var(code, "TCPI_OPT_SACK", TCPI_OPT_SACK);
> > >  #endif  /* linux */
> > >  }
> >
> > Sure! Done. I added all the missing bit values in the following commit:
> >
> > https://github.com/google/packetdrill/commit/faa0dfb54065118625e169d3111ce09c65b20229
> >
> > This can be picked up with the following, or similar:
> >
> >   git clone https://github.com/google/packetdrill.git
>
> Updated in netdev CI.

Excellent, thanks Neal and Jakub.

I am sending a V2 right now, because I am OOO for the rest of the week.