Re: [PATCH net] selftests: forwarding: local_termination: fix PTP UDP cksums

[Alexander Sverdlin <alexander.sverdlin@gmail.com>]

Hi Daniel,

On Sat, 2026-03-21 at 04:26 +0000, Daniel Golle wrote:
> All six PTP-over-IP test frames (3x IPv4 + 3x IPv6) contain incorrect
> UDP checksums. The stored values are the ones-complement sums of just
> the pseudo-headers, not the complete UDP checksums over pseudo-header +
> UDP header + payload. This is characteristic of frames captured on the
> sender before TX checksum offload completion.
> 
> For example, the IPv4 Sync and Follow-Up frames both store checksum
> 0xa3c8 despite having different UDP payloads and port numbers - 0xa3c8
> is their shared pseudo-header sum (same src/dst IP, same protocol and
> UDP length).
> 
> While most L2 switches forward frames without verifying transport
> checksums, hardware that performs deep packet inspection or has PTP
> awareness may validate UDP checksums and drop frames that fail
> verification. This causes the 1588v2 over IPv4/IPv6 tests to fail on
> such hardware even though L2 PTP (which has no UDP checksum) passes
> fine.
> 
> Replace all six pseudo-header partial sums with the correctly computed
> full UDP checksums:
> 
>   IPv4 Sync:           0xa3c8 -> 0x9f41
>   IPv4 Follow-Up:      0xa3c8 -> 0xeb8a
>   IPv4 Peer Delay Req: 0xa2bc -> 0x9ab9
>   IPv6 Sync:           0x2e92 -> 0x1476
>   IPv6 Follow-Up:      0x2e92 -> 0xf047
>   IPv6 Peer Delay Req: 0xb454 -> 0x891f
> 
> Fixes: 2379795042649 ("selftests: net: local_termination: add PTP frames to the mix")
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>

wireshark agrees,

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>

> ---
>  .../selftests/net/forwarding/local_termination.sh    | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/forwarding/local_termination.sh b/tools/testing/selftests/net/forwarding/local_termination.sh
> index 9bc9d25e71368..15b1a1255a41f 100755
> --- a/tools/testing/selftests/net/forwarding/local_termination.sh
> +++ b/tools/testing/selftests/net/forwarding/local_termination.sh
> @@ -57,21 +57,21 @@ PTP_1588_L2_PDELAY_REQ=" \
>  PTP_1588_IPV4_SYNC=" \
>  01:00:5e:00:01:81 00:00:de:ad:be:ef 08:00 45 00 \
>  00 48 0a 9a 40 00 01 11 cb 88 c0 00 02 01 e0 00 \
> -01 81 01 3f 01 3f 00 34 a3 c8 00 02 00 2c 00 00 \
> +01 81 01 3f 01 3f 00 34 9f 41 00 02 00 2c 00 00 \
>  02 00 00 00 00 00 00 00 00 00 00 00 00 00 3e 37 \
>  63 ff fe cf 17 0e 00 01 00 00 00 00 00 00 00 00 \
>  00 00 00 00 00 00"
>  PTP_1588_IPV4_FOLLOW_UP="
>  01:00:5e:00:01:81 00:00:de:ad:be:ef 08:00 45 00 \
>  00 48 0a 9b 40 00 01 11 cb 87 c0 00 02 01 e0 00 \
> -01 81 01 40 01 40 00 34 a3 c8 08 02 00 2c 00 00 \
> +01 81 01 40 01 40 00 34 eb 8a 08 02 00 2c 00 00 \
>  00 00 00 00 00 00 00 00 00 00 00 00 00 00 3e 37 \
>  63 ff fe cf 17 0e 00 01 00 00 02 00 00 00 66 83 \
>  c6 0f 1d 9a 61 87"
>  PTP_1588_IPV4_PDELAY_REQ=" \
>  01:00:5e:00:00:6b 00:00:de:ad:be:ef 08:00 45 00 \
>  00 52 35 a9 40 00 01 11 a1 85 c0 00 02 01 e0 00 \
> -00 6b 01 3f 01 3f 00 3e a2 bc 02 02 00 36 00 00 \
> +00 6b 01 3f 01 3f 00 3e 9a b9 02 02 00 36 00 00 \
>  00 00 00 00 00 00 00 00 00 00 00 00 00 00 3e 37 \
>  63 ff fe cf 17 0e 00 01 00 01 05 7f 00 00 00 00 \
>  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00"
> @@ -79,7 +79,7 @@ PTP_1588_IPV6_SYNC=" \
>  33:33:00:00:01:81 00:00:de:ad:be:ef 86:dd 60 06 \
>  7c 2f 00 36 11 01 20 01 0d b8 00 01 00 00 00 00 \
>  00 00 00 00 00 01 ff 0e 00 00 00 00 00 00 00 00 \
> -00 00 00 00 01 81 01 3f 01 3f 00 36 2e 92 00 02 \
> +00 00 00 00 01 81 01 3f 01 3f 00 36 14 76 00 02 \
>  00 2c 00 00 02 00 00 00 00 00 00 00 00 00 00 00 \
>  00 00 3e 37 63 ff fe cf 17 0e 00 01 00 00 00 00 \
>  00 00 00 00 00 00 00 00 00 00 00 00"
> @@ -87,7 +87,7 @@ PTP_1588_IPV6_FOLLOW_UP=" \
>  33:33:00:00:01:81 00:00:de:ad:be:ef 86:dd 60 0a \
>  00 bc 00 36 11 01 20 01 0d b8 00 01 00 00 00 00 \
>  00 00 00 00 00 01 ff 0e 00 00 00 00 00 00 00 00 \
> -00 00 00 00 01 81 01 40 01 40 00 36 2e 92 08 02 \
> +00 00 00 00 01 81 01 40 01 40 00 36 f0 47 08 02 \
>  00 2c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
>  00 00 3e 37 63 ff fe cf 17 0e 00 01 00 00 02 00 \
>  00 00 66 83 c6 2a 32 09 bd 74 00 00"
> @@ -95,7 +95,7 @@ PTP_1588_IPV6_PDELAY_REQ=" \
>  33:33:00:00:00:6b 00:00:de:ad:be:ef 86:dd 60 0c \
>  5c fd 00 40 11 01 fe 80 00 00 00 00 00 00 3c 37 \
>  63 ff fe cf 17 0e ff 02 00 00 00 00 00 00 00 00 \
> -00 00 00 00 00 6b 01 3f 01 3f 00 40 b4 54 02 02 \
> +00 00 00 00 00 6b 01 3f 01 3f 00 40 89 1f 02 02 \
>  00 36 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
>  00 00 3e 37 63 ff fe cf 17 0e 00 01 00 01 05 7f \
>  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \

-- 
Alexander Sverdlin.