Packetdrill's concise user guide

/* Set the offload flags to be like a typical ethernet device */
static void set_device_offload_flags(struct local_netdev *netdev)
{
#ifdef linux
// const u32 offload =
// TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 | TUN_F_TSO_ECN | TUN_F_UFO;
// if (ioctl(netdev->tun_fd, TUNSETOFFLOAD, offload) != 0)
// die_perror("TUNSETOFFLOAD");
#endif
}

./packetdrill test.pkt

// Test fast retransmit with 4 packets outstanding, receiver sending SACKs.
// In this variant the receiver supports SACK.
// 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
//Three-way handshake+0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
+0 > S. 0:0(0) ack 1 <...>
+.1 < . 1:1(0) ack 1 win 257
+0 accept(3, ..., ...) = 4
// System call, let the protocol stack send 100 bytes // Send 1 data segment and get an ACK, so cwnd is now 4.
+0 write(4, ..., 1000) = 1000
//The protocol stack is expected to send psh, ack, but it actually sends ack1
//+0 > P. 1:1001(1000) ack 2
//Inject ack into the protocol stack
+.1 < . 1:1(0) ack 1001 win 257
// Write 4 data segments.
//System call, let the protocol stack send 4000 bytes + 0 write(4, ..., 4000) = 4000
//The protocol stack is expected to send psh, ack, but it actually sends seq 1001:2001, ack 1; seq 2001:3001, ack 1; seq 3001:4001, ack 1; [P.], seq 4001:5001, ack 1
//+0 > P. 1001:5001(4000) ack 1
// Get 3 SACKs.
//Send three acks to the protocol stack in succession
+.1 < . 1:1(0) ack 1001 win 257 <sack 2001:3001,nop,nop>
+0 < . 1:1(0) ack 1001 win 257 <sack 2001:4001,nop,nop>
+0 < . 1:1(0) ack 1001 win 257 <sack 2001:5001,nop,nop>
// We've received 3 duplicate ACKs, so we do a fast retransmit.
//The protocol stack is expected to issue a fast retransmit Seq 1001:2001, ack 1
//+0 > . 1001:2001(1000) ack 1
// Receiver ACKs all data.
//ACK to the protocol stack and respond to the ACK of all messages.
+.1 < . 1:1(0) ack 6001 win 257
4. Modify fr-4pkt-sack-linux.pkt as follows.
+0 > P. 1:1001(1000) ack 2  +0 > P. 1:1001(1000) ack 1
//+0 > P. 1001:5001(4000) ack 1  
+0 > . 1001:2001(1000) ack 1
+0 > . 2001:3001(1000) ack 1
+0 > . 3001:4001(1000) ack 1
+0 > P. 4001:5001(1000) ack 1

// Construct the packet yourself to implement three repeated ack 1001.
07:57:36.469280 IP 192.0.2.1.36840 > TENCENT64.site.webcache: Flags [.], ack 1001, win 257, options [sack 1 {2001:3001},nop,nop], length 0
07:57:36.469836 IP 192.0.2.1.36840 > TENCENT64.site.webcache: Flags [.], ack 1001, win 257, options [sack 1 {2001:4001},nop,nop], length 0
07:57:36.470349 IP 192.0.2.1.36840 > TENCENT64.site.webcache: Flags [.], ack 1001, win 257, options [sack 1 {2001:5001},nop,nop], length 0
// The protocol stack initiates fast retransmission. Seq 1001:2001,ack 1,1000
07:57:36.470376 IP TENCENT64.site.webcache > 192.0.2.1.36840: Flags [.], seq 1001:2001, ack 1, win 229, length 1000

0.100 < S 0:0(0) win 32792 <mss 1000, nop, nop, sackOK, nop, wscale 7>
0.250 < [1:1461(1460)] icmp unreachable frag_needed mtu 1200

+0 > udp (1472)

connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress) //Client connects to server getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0 //Get socketopt
fcntl(3, F_SETFL, O_RDWR) = 0 //Fcntl settings ioctl(4, SIOCINQ, [1000]) = 0 //Ioctl settings read(3, ..., 1024) = 785 //Read data write(3, ..., 57) = 57 //Write data close(3) = 0 //Close the connection socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 //Tcp socket
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 //Set address reuse bind(3, ..., ...) = 0 //Bind port listen(3, 1) = 0 //Listen port accept(3, ..., ...) = 4 //Accept connection

+0 `sysctl -q net.ipv4.tcp_timestamps=0`
+0 `ss -4 -n state SYN-RECV | grep 192.168.0.1:8080 > /dev/null`

0.310%
assert tcpi_reordering == 3
assert tcpi_unacked == 10
assert tcpi_sacked == 6
assert tcpi_ca_state == TCP_CA_Recovery
}%

Absolute: 0.75
Relative: +0.2
Wildcard (any time):*
Range (absolute time interval): 0.750~0.900
Relative Range: +0.1~+0.2
Loose (allowable error value): --tolerance_usecs=800
Blocking (blocking time interval): 0.750...0.900

+1.0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6>

// Establish a connection.
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
0.000 bind(3, ..., ...) = 0
0.000 listen(3, 1) = 0
0.000...0.200 accept(3, ..., ...) = 4
0.100 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
0.100 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 6>
0.200 < . 1:1(0) ack 1 win 257
//The server calls the system call and expects to send 2 packets.
0.300 write(4, ..., 2000) = 2000
//0.300 > P. 1:2001(2000) ack 1
0.300 > . 1:1001(1000) ack 1
0.300 > P. 1001:2001(1000) ack 1

// Create a socket and set it to non-blocking.
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
0.000 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
// Establish connection and verify that there was no error.
0.100 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
0.100 > S 0:0(0) <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 6>
0.200 < S. 0:0(0) ack 1 win 5792 <mss 1460,sackOK,TS val 700 ecr 100,nop,wscale 7>
0.200 > . 1:1(0) ack 1 <nop,nop,TS val 200 ecr 700>
//The client calls the system call, expecting to make an http request.
// Send the HTTP request.
0.200 write(3, ..., 57) = 57
0.200 > P. 1:58(57) ack 1 <nop,nop,TS val 200 ecr 700>
0.300 < . 1:1(0) ack 58 win 92 <nop,nop,TS val 800 ecr 200>