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// Test Path MTU discovery, RFC 1191.
// This is a simple case, with one packet to send.
// In this variant, we get an ICMP "unreachable frag_needed mtu 1200"
// message and because the TCP sequence number is valid, TCP
// immediately retransmits our first outstanding packet
// with a smaller MSS based on the MTU from the ICMP message.
// 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
0.100 < S 0:0(0) win 32792 <mss 1460,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
0.200 accept(3, ..., ...) = 4
// Send 1 data segment.
0.200 write(4, ..., 1460) = 1460
0.200 > P. 1:1461(1460) ack 1
// ICMP says that segment was too big.
0.250 < [1:1461(1460)] icmp unreachable frag_needed mtu 1200
// TCP picks a packet size using the MTU from the message, and retransmits.
0.250 > . 1:1161(1160) ack 1
0.250 > P. 1161:1461(300) ack 1
// Receiver ACKs all data.
0.350 < . 1:1(0) ack 1461 win 257
// Clean up.
1.300 close(4) = 0
1.300 > F. 1461:1461(0) ack 1
1.400 < F. 1:1(0) ack 1462 win 257
1.400 > . 1462:1462(0) ack 2
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