Open Menu / tools / testing / selftests / net / packetdrill / tcp_rcv_wnd_shrink_allowed.pkt 
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// SPDX-License-Identifier: GPL-2.0

--mss=1000

`./defaults.sh
sysctl -q net.ipv4.tcp_shrink_window=1
sysctl -q net.ipv4.tcp_rmem="4096 32768 $((32*1024*1024))"`

   0 `nstat -n`

// Establish a connection.
  +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 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
  +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 10>
  +0 < . 1:1(0) ack 1 win 257

  +0 accept(3, ..., ...) = 4

  +0 < P. 1:10001(10000) ack 1 win 257
   * > .  1:1(0) ack 10001 win 15

  +0 < P. 10001:11024(1023) ack 1 win 257
   * > .  1:1(0) ack 11024 win 13

// Max window seq advertised 10001 + 15*1024 = 25361, last advertised: 11024 + 13*1024 = 24336

// Segment beyond the max window is dropped
  +0 < P. 11024:25362(14338) ack 1 win 257
   * > .  1:1(0) ack 11024 win 13

// Segment using the max window is accepted
  +0 < P. 11024:25361(14337) ack 1 win 257
   * > .  1:1(0) ack 25361 win 0

// Check LINUX_MIB_BEYOND_WINDOW has been incremented once
  +0 `nstat | grep TcpExtBeyondWindow | grep -q " 1 "`