Messages in this thread | | | Subject | Nfs over tcp retries | Date | Mon, 5 Mar 2007 10:42:53 -0000 | From | "Andy Chittenden" <> |
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Here's a sequence of packets captured at the end of a NFS connection and the start of the next for a RH Fedora Core 6 client:
# cat ~/tmp/28852a.txt No. Time Source Destination Protocol Info 1 0.000000 192.168.37.10 192.168.38.218 TCP 894 > nfs [ACK] Seq=4104776783 Ack=146337374 Win=5840 Len=1460 2 0.000009 192.168.37.10 192.168.38.218 TCP 894 > nfs [PSH, ACK] Seq=4104778243 Ack=146337374 Win=5840 Len=1244[Packet size limited during capture] 3 0.000031 192.168.38.218 192.168.37.10 TCP nfs > 894 [FIN, ACK] Seq=146337374 Ack=4104776783 Win=64240 Len=0 4 0.000210 192.168.38.218 192.168.37.10 TCP nfs > 894 [ACK] Seq=146337375 Ack=4104779487 Win=64240 Len=0 5 0.000226 192.168.37.10 192.168.38.218 TCP 894 > nfs [ACK] Seq=4104779487 Ack=146337375 Win=5840 Len=0 6 0.002454 192.168.37.10 192.168.38.218 TCP 894 > nfs [FIN, ACK] Seq=4104779487 Ack=146337375 Win=5840 Len=0 7 0.002651 192.168.38.218 192.168.37.10 TCP nfs > 894 [ACK] Seq=146337375 Ack=4104779488 Win=64240 Len=0 8 0.003601 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775174 Len=0 MSS=1460 TSV=110286926 TSER=0 WS=7 9 0.003709 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775175 Win=64240 Len=0 10 3.003081 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775177 Len=0 MSS=1460 TSV=110287676 TSER=0 WS=7 11 3.003196 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775178 Win=64240 Len=0 12 9.003738 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775180 Len=0 MSS=1460 TSV=110289176 TSER=0 WS=7 13 9.003852 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775181 Win=64240 Len=0 14 21.004805 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775183 Len=0 MSS=1460 TSV=110292177 TSER=0 WS=7 15 21.004917 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775184 Win=64240 Len=0 16 45.007926 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775186 Len=0 MSS=1460 TSV=110298177 TSER=0 WS=7 17 45.008050 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775187 Win=64240 Len=0 18 93.005802 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775189 Len=0 MSS=1460 TSV=110310177 TSER=0 WS=7 19 93.005933 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775190 Win=64240 Len=0 20 189.009560 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775192 Len=0 MSS=1460 TSV=110334177 TSER=0 WS=7 21 189.009675 192.168.38.218 192.168.37.10 TCP nfs > 894 [RST, ACK] Seq=146337375 Ack=4104775193 Win=64240 Len=0 22 381.013870 192.168.37.10 192.168.38.218 TCP 894 > nfs [SYN] Seq=4104775195 Len=0 MSS=1460 TSV=110382178 TSER=0 WS=7 23 381.013980 192.168.38.218 192.168.37.10 TCP [TCP Previous segment lost] nfs > 894 [SYN, ACK] Seq=240134139 Ack=4104775196 Win=64240 Len=0 MSS=1460 24 381.014010 192.168.37.10 192.168.38.218 TCP 894 > nfs [ACK] Seq=4104775196 Ack=240134140 Win=5840 Len=0
As you can see in packet 3, the nfs server's sent a FIN-ACK which is acknowledged in packet 6 by the client. So by packet 8, the connection's closed. The client attempts to reconnect to the server in packet 8 which is refused by the server in packet 9 as the client is using the same port number as the previous session: the server's in TIME WAIT from the previous connection and the initial send sequence number of this new connection is below the highest sequence number of the previous connection. The client's attempts to reconnect continue unsuccessfully until 2MSL is exceeded.
So, a few questions:
* why does the NFS client reuse the same source port number (894 in the example above)? * if the socket's being reused, why is the ISS being chosen such that it's within the same range as the last successful connection? * why does the ISS seem to go up by only 3 since the last attempt to connect?
If the linux NFS client had used a different source port number or chosen an out-of-range ISS, then its reconnection attempts would have been successful in a more timely manner.
-- Andy, BlueArc Engineering - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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