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sent-too-much-sack-optlen.pkt
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Sun, Oct 11, 8:45 PM
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sent-too-much-sack-optlen.pkt
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// Limited transmit KASSERT "sent too much" from tcp_maxseg() overestimating
// SACK option space: no timestamps, five SACK blocks pending, one full
// segment sent after an RTO. Panics an INVARIANTS kernel without the fix.
--ip_version=ipv4
0.000 `sysctl -w net.inet.tcp.hostcache.purgenow=1`
+0.000 `sysctl -w net.inet.tcp.syncookies_only=0`
+0.000 `sysctl -w net.inet.tcp.syncookies=1`
+0.000 `sysctl -w net.inet.tcp.sack.enable=1`
+0.000 `sysctl -w net.inet.tcp.functions_default=freebsd`
+0.000 `sysctl -w net.inet.tcp.cc.algorithm=cubic`
+0.000 `sysctl -w kern.timecounter.alloweddeviation=0`
+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
// No timestamps, no window scaling; t_maxseg = 1000.
+0.000 < S 0:0(0) win 65535 <mss 1000,sackOK,eol,eol>
+0.000 > S. 0:0(0) ack 1 win 65535 <...>
+0.050 < . 1:1(0) ack 1 win 65535
+0.000 accept(3, ..., ...) = 4
+0.000 close(3) = 0
// Five out-of-order blocks: rcv_numsacks = 5, only 4 fit on the wire.
+0.000 < . 101:201(100) ack 1 win 65535
+0.000 > . 1:1(0) ack 1 <...>
+0.000 < . 301:401(100) ack 1 win 65535
+0.000 > . 1:1(0) ack 1 <...>
+0.000 < . 501:601(100) ack 1 win 65535
+0.000 > . 1:1(0) ack 1 <...>
+0.000 < . 701:801(100) ack 1 win 65535
+0.000 > . 1:1(0) ack 1 <...>
+0.000 < . 901:1001(100) ack 1 win 65535
+0.000 > . 1:1(0) ack 1 <...>
// One small segment, lost; the RTO leaves cwnd = 1000, t_rxtshift = 1.
+0.000 send(4, ..., 300, 0) = 300
+0.000 > P. 1:301(300) ack 1 <...>
+1.000~+1.200 > P. 1:301(300) ack 1 <...>
// 700 bytes of cwnd left, below a full segment, so Nagle holds the rest.
+0.010 send(4, ..., 5000, 0) = 5000
// First dup ACK: limited transmit sends one full 964-byte segment
// (1000 - 36 bytes of options), while tcp_maxseg() said 960.
+0.010 < . 1:1(0) ack 1 win 65535 <nop,nop,sack 101:301>
+0.000 > . 301:1265(964) ack 1 <...>

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