Files
linux-net/tools/testing/selftests/net/packetdrill/tcp_accecn_synack_rxmt.pkt
Chia-Yu Chang f85d9c45f1 selftests/net: packetdrill: add TCP Accurate ECN cases
Linux Accurate ECN test sets using ACE counters and AccECN options to
cover several scenarios: Connection teardown, different ACK conditions,
counter wrapping, SACK space grabbing, fallback schemes, negotiation
retransmission/reorder/loss, AccECN option drop/loss, different
handshake reflectors, data with marking, and different sysctl values.

The packetdrill used is commit cbe405666c9c8698ac1e72f5e8ffc551216dfa56
of repo: https://github.com/minuscat/packetdrill/tree/upstream_accecn.
And corresponding patches are sent to google/packetdrill email list.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Co-developed-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Co-developed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131222515.8485-16-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2026-02-03 15:13:25 +01:00

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// Test that we retransmit SYN-ACK with ACE and without
// AccECN options after
// SYN-ACK was lost and TCP moved to TCPS_SYN_RECEIVED
`./defaults.sh
sysctl -q net.ipv4.tcp_ecn=3
sysctl -q net.ipv4.tcp_ecn_option=2
`
+0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0
+0 < [noecn] SEWA 0:0(0) win 32792 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+.002 > [noecn] SW. 0:0(0) ack 1 <mss 1460,ECN e1b 1 ceb 0 e0b 1,nop,nop,nop,sackOK,nop,wscale 8>
// Retransmit SYN-ACK without option
+1~+1.1 > [noecn] SW. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+0.1 < [noecn] W. 1:1(0) ack 1 win 320 <ECN e0b 1 ceb 0 e1b 1,nop>
+.002 accept(3, ..., ...) = 4
// We try to write with AccECN option
+0.01 write(4, ..., 100) = 100
+.002 > [ect0] P5. 1:101(100) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop>