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• ftp connection problem, vsftp server, active mode

  - by Mark Szente

  I have a server that runs vsftpd to handle ftp connections. One of my users have a notebook with Total Commander and WinSCP installed. Both ftp clients fail right after the connection is established to the server and it tries to download the directory listing with the following error message: Timeout detected. Could not retrieve directory listing PORT command successful. Consider using PASV. Error listing directory '/'. The weird thing is: the notebook works perfectly ok with other ftp servers. My ftp server also works well with other clients. In fact, this user also has a pc running on the same LAN as the notebook and the pc works well with the ftp server. We use PORT ftp connection mode. Passive mode works well but is not an option at this point. I would post more technical details but I don't even know what this problem is related to. Anyway, below is the server side tcpdump for the failed connection attempt. There's no further communication between the client and the server after the last line of log. Thank you very much for any hint! 23:39:24.514852 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: S 1314489715:1314489715(0) win 65535 <mss 1460,nop,wscale 3,nop,nop,sackOK> 23:39:24.514896 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: S 2633658883:2633658883(0) ack 1314489716 win 5840 <mss 1460,nop,nop,sackOK,nop,wscale 2> 23:39:24.520842 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: . ack 1 win 62500 23:39:24.523803 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 1:21(20) ack 1 win 1460 23:39:24.546858 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 1:15(14) ack 21 win 62497 23:39:24.546902 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: . ack 15 win 1460 23:39:24.547247 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 21:55(34) ack 15 win 1460 23:39:24.762806 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: . ack 55 win 62493 23:39:30.415011 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 15:28(13) ack 55 win 62493 23:39:30.454116 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: . ack 28 win 1460 23:39:31.036283 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 55:78(23) ack 28 win 1460 23:39:31.053018 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 28:34(6) ack 78 win 62490 23:39:31.053042 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: . ack 34 win 1460 23:39:31.053268 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 78:97(19) ack 34 win 1460 23:39:31.068969 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 34:40(6) ack 97 win 62488 23:39:31.069148 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 97:112(15) ack 40 win 1460 23:39:31.069179 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 112:119(7) ack 40 win 1460 23:39:31.076981 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: . ack 119 win 62485 23:39:31.077010 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 119:177(58) ack 40 win 1460 23:39:31.114979 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 40:45(5) ack 177 win 62478 23:39:31.115164 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 177:186(9) ack 45 win 1460 23:39:31.180966 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 45:53(8) ack 186 win 62476 23:39:31.181066 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 186:216(30) ack 53 win 1460 23:39:31.213065 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 53:80(27) ack 216 win 62473 23:39:31.213180 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 216:267(51) ack 80 win 1460 23:39:31.251086 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: P 80:86(6) ack 267 win 62466 23:39:31.251498 IP 195.70.xx.xx.20 > 62.201.xx.xx.5001: S 2640780713:2640780713(0) win 5840 <mss 1460,sackOK,timestamp 2054371220 0,nop,wscale 2> 23:39:31.290979 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: . ack 86 win 1460 23:39:34.251489 IP 195.70.xx.xx.20 > 62.201.xx.xx.5001: S 2640780713:2640780713(0) win 5840 <mss 1460,sackOK,timestamp 2054374220 0,nop,wscale 2> 23:39:40.249625 IP 195.70.xx.xx.20 > 62.201.xx.xx.5001: S 2640780713:2640780713(0) win 5840 <mss 1460,sackOK,timestamp 2054380220 0,nop,wscale 2> 23:39:43.695108 IP 195.70.xx.xx.21 > 62.201.xx.xx.1057: P 2280716551:2280716588(37) ack 3838413728 win 5840 23:39:52.248791 IP 195.70.xx.xx.20 > 62.201.xx.xx.5001: S 2640780713:2640780713(0) win 5840 <mss 1460,sackOK,timestamp 2054392220 0,nop,wscale 2> 23:40:16.245159 IP 195.70.xx.xx.20 > 62.201.xx.xx.5001: S 2640780713:2640780713(0) win 5840 <mss 1460,sackOK,timestamp 2054416221 0,nop,wscale 2> 23:40:29.853685 IP 195.70.xx.xx.21 > 62.201.xx.xx.1057: FP 37:51(14) ack 1 win 5840 23:40:31.241951 IP 195.70.xx.xx.21 > 62.201.xx.xx.2241: P 267:304(37) ack 86 win 1460 23:40:31.381708 IP 62.201.xx.xx.2241 > 195.70.xx.xx.21: . ack 304 win 62462

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• TCP connection stuck in SYN_RECV state despite ACK received, Linux 2.6.18, embedded, ARM

  - by waynix

  My client cannot connect to my protocol port (TCP) after some network glitches, even though all other protocols (telnet/HTTP/FTP) work fine. netstat shows that my server is listening and tcpdump on the server shows all 3 packets are exchanged: 18:29:16.578964 IP 10.9.59.10.3355 10.9.43.131.5084: S 2602965897:2602965897(0) win 65535 <mss 1460,nop,nop,sackOK> 18:29:16.579107 IP 10.9.43.131.5084 10.9.59.10.3355: S 3464857909:3464857909(0) ack 2602965898 win 5840 <mss 1460,nop,nop,sackOK> 18:29:16.579284 IP 10.9.59.10.3355 10.9.43.131.5084: . ack 1 win 65535 But somehow netstat -t shows the connection still in SYN_RECV, as if the ack is not seen by the TCP state machine. I have to restart my server to get it to work. syncookie is not enabled, and I know from client code behavior and tcpdump that there is no SYN flooding. Help much appreciated.

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• ack (perl?) regexp matching lines where if is the first word

  - by Gauthier

  Hey. I'm finally learning regexps, training with ack. I believe this uses perl regexp. I want to match all lines where the first non-blank characters are if (<word> !, with any number of spaces in between the elements. This is what I came up with: ^[ \t]*if *\(\w+ *! It only nearly worked. ^[ \t]* is wrong, since it matches one or none [space or tab]. What I want is to match anything that may contain only space or tab (or nothing). For example these should not match: // if (asdf != 0) else if (asdf != 1) How can I modify my regexp for that?

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• Change TCP wait for ACK timeouts in Win7/WinServer

  - by maseth

  Is there any possibility to change default wait for ACK timeout in TCP network on Windows 7 or Windows Server ? I'm using very slow network ( 1200 bps ) and want to tweak TCP. When using default parameters network stuck on multiple retransmissions . If I'm able to change the ACK timeout and tx window size I think that it would work. On Windows XP it was possible but cant find any document for Win7 and Win Server.

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• "Google files": Building a web interface to find/ack/grep

  - by user27915816

  I am working on a project where we would like to have build a web interface that gives the user the ability to "Google" files in a directory in a remote machine. For example, the user would type a string in a box, and then the system would find all files that contain that string and present them in the browser. The system would then give the user the ability click on any of the files to open them/display them in the browser. We want to avoid reinventing the wheel if possible, but don't really know where to start (none of us in the team have much experience building websites). What software packages, libraries or tools exist that can help us get this done?

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• server dosnt produce syn-ack

  - by steve

  I have a small program that take packets from the nfqueue . change the ip.dst to my server dst (and ttl), recalc checksum and return the packet to the nfqueue. The server and the client are linux and apache web server is run on the server and listen on port 80. i open telnet in the client to fake ip on port 80 . the packet is changed by my program and sent to the server, but the target server (the new dst ip) get the syn , but dosnt generate syn-ack (the server also belong to me , so i can see that it get the syn with checksum correct , but dosnt generate syn-ack). if i do the same , but with the real server ip as the dest, the tcp handshake is done correct (in this case i just change the ttl and checksum. The change that i did to the ttl is just a test to see that my checksum calc is ok). i compare the sys's , but didnt find and difference. Any idea? Ps. i saw this topic : Server not sending a SYN/ACK packet in response to a SYN packet and i set all flags the same , but this didnt help. Thank you

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• SSL / HTTP / No Response to Curl

  - by Alex McHale

  I am trying to send commands to a SOAP service, and getting nothing in reply. The SOAP service is at a completely separate site from either server I am testing with. I have written a dummy script with the SOAP XML embedded. When I run it at my local site, on any of three machines -- OSX, Ubuntu, or CentOS 5.3 -- it completes successfully with a good response. I then sent the script to our public host at Slicehost, where I fail to get the response back from the SOAP service. It accepts the TCP socket and proceeds with the SSL handshake. I do not however receive any valid HTTP response. This is the case whether I use my script or curl on the command line. I have rewritten the script using SOAP4R, Net::HTTP and Curb. All of which work at my local site, none of which work at the Slicehost site. I have tried to assemble the CentOS box as closely to match my Slicehost server as possible. I rebuilt the Slice to be a stock CentOS 5.3 and stock CentOS 5.4 with the same results. When I look at a tcpdump of the bad sessions on Slicehost, I see my script or curl send the XML to the remote server, and nothing comes back. When I look at the tcpdump at my local site, I see the response just fine. I have entirely disabled iptables on the Slice. Does anyone have any ideas what could be causing these results? Please let me know what additional information I can furnish. Thank you! Below is a wire trace of a sample session. The IP that starts with 173 is my server while the IP that starts with 12 is the SOAP server's. No. Time Source Destination Protocol Info 1 0.000000 173.45.x.x 12.36.x.x TCP 36872 > https [SYN] Seq=0 Win=5840 Len=0 MSS=1460 TSV=137633469 TSER=0 WS=6 Frame 1 (74 bytes on wire, 74 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 0, Len: 0 No. Time Source Destination Protocol Info 2 0.040000 12.36.x.x 173.45.x.x TCP https > 36872 [SYN, ACK] Seq=0 Ack=1 Win=8760 Len=0 MSS=1460 Frame 2 (62 bytes on wire, 62 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Info 3 0.040000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=1 Ack=1 Win=5840 Len=0 Frame 3 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Info 4 0.050000 173.45.x.x 12.36.x.x SSLv2 Client Hello Frame 4 (156 bytes on wire, 156 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 1, Ack: 1, Len: 102 Secure Socket Layer No. Time Source Destination Protocol Info 5 0.130000 12.36.x.x 173.45.x.x TCP [TCP segment of a reassembled PDU] Frame 5 (1434 bytes on wire, 1434 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 1, Ack: 103, Len: 1380 Secure Socket Layer No. Time Source Destination Protocol Info 6 0.130000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=103 Ack=1381 Win=8280 Len=0 Frame 6 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 1381, Len: 0 No. Time Source Destination Protocol Info 7 0.130000 12.36.x.x 173.45.x.x TLSv1 Server Hello, Certificate, Server Hello Done Frame 7 (1280 bytes on wire, 1280 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 1381, Ack: 103, Len: 1226 [Reassembled TCP Segments (2606 bytes): #5(1380), #7(1226)] Secure Socket Layer No. Time Source Destination Protocol Info 8 0.130000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=103 Ack=2607 Win=11040 Len=0 Frame 8 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 2607, Len: 0 No. Time Source Destination Protocol Info 9 0.130000 173.45.x.x 12.36.x.x TLSv1 Client Key Exchange, Change Cipher Spec, Encrypted Handshake Message Frame 9 (236 bytes on wire, 236 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 2607, Len: 182 Secure Socket Layer No. Time Source Destination Protocol Info 10 0.190000 12.36.x.x 173.45.x.x TLSv1 Change Cipher Spec, Encrypted Handshake Message Frame 10 (97 bytes on wire, 97 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2607, Ack: 285, Len: 43 Secure Socket Layer No. Time Source Destination Protocol Info 11 0.190000 173.45.x.x 12.36.x.x TLSv1 Application Data Frame 11 (347 bytes on wire, 347 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 285, Ack: 2650, Len: 293 Secure Socket Layer No. Time Source Destination Protocol Info 12 0.190000 173.45.x.x 12.36.x.x TCP [TCP segment of a reassembled PDU] Frame 12 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 13 0.450000 12.36.x.x 173.45.x.x TCP https > 36872 [ACK] Seq=2650 Ack=578 Win=64958 Len=0 Frame 13 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2650, Ack: 578, Len: 0 No. Time Source Destination Protocol Info 14 0.450000 173.45.x.x 12.36.x.x TCP [TCP segment of a reassembled PDU] Frame 14 (206 bytes on wire, 206 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 2038, Ack: 2650, Len: 152 No. Time Source Destination Protocol Info 15 0.510000 12.36.x.x 173.45.x.x TCP [TCP Dup ACK 13#1] https > 36872 [ACK] Seq=2650 Ack=578 Win=64958 Len=0 Frame 15 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2650, Ack: 578, Len: 0 No. Time Source Destination Protocol Info 16 0.850000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 16 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 17 1.650000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 17 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 18 3.250000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 18 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 19 6.450000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 19 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer

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• NFS issue: clients can mount shares as NFSv3 but not as NFSv4 -- or how to debug NFS?

  - by tdn

  Problem description I have a file server running Debian. On it I have a few NFS shares. When I mount the shares from a client using NFSv3 (mount.nfs 10.0.0.51:/exports/video /mnt -o vers=3,soft,intr,timeo=10), it works. However, I would like to use NFSv4 because of improved security and performance. When I try to mount an NFSv4 share on malbec the mount command just hangs and finally times out after 2 minutes. How do I make the clients mount the NFSv4 shares as NFSv4? How do I troubleshoot NFS? There is no information in the syslog on neither client nor server. What are any errors in my configuration? Facts: Server is corvina(10.0.0.51) Client is malbec(10.0.0.1) Malbec runs Ubuntu 12.04 Server runs Debian 7 wheezy Both are connected through 1 GbE LAN. Firewalls are off. rpcinfo (root@malbec) (13-07-02 21:00) (P:0 L:1) [0] ~ # rpcinfo -p program vers proto port service 100000 4 tcp 111 portmapper 100000 3 tcp 111 portmapper 100000 2 tcp 111 portmapper 100000 4 udp 111 portmapper 100000 3 udp 111 portmapper 100000 2 udp 111 portmapper 100024 1 udp 4000 status 100024 1 tcp 4000 status (root@malbec) (13-07-02 21:00) (P:0 L:1) [0] ~ # rpcinfo -p corvina program vers proto port service 100000 4 tcp 111 portmapper 100000 3 tcp 111 portmapper 100000 2 tcp 111 portmapper 100000 4 udp 111 portmapper 100000 3 udp 111 portmapper 100000 2 udp 111 portmapper 100024 1 udp 4000 status 100024 1 tcp 4000 status 100003 3 udp 2049 nfs 100227 3 udp 2049 100021 1 udp 4003 nlockmgr 100021 3 udp 4003 nlockmgr 100021 4 udp 4003 nlockmgr 100021 1 tcp 4003 nlockmgr 100021 3 tcp 4003 nlockmgr 100021 4 tcp 4003 nlockmgr 100005 1 udp 4002 mountd 100005 1 tcp 4002 mountd 100005 2 udp 4002 mountd 100005 2 tcp 4002 mountd 100005 3 udp 4002 mountd 100005 3 tcp 4002 mountd tcpdump The following is output from tcpdump on malbec while running this command: # rpcinfo -p corvina ~ # tcpdump -i eth0 host 10.0.0.51 21:14:51.762083 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [S], seq 3069120722, win 14600, options [mss 1460,sackOK,TS val 146111 ecr 0,nop,wscale 7], length 0 21:14:51.762431 IP corvina.vineyard.sikkerhed.org.sunrpc > malbec.vineyard.sikkerhed.org.948: Flags [S.], seq 770684199, ack 3069120723, win 14480, options [mss 1460,sackOK,TS val 398850 ecr 146111,nop,wscale 7], length 0 21:14:51.762458 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [.], ack 1, win 115, options [nop,nop,TS val 146111 ecr 398850], length 0 21:14:51.762556 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [P.], seq 1:45, ack 1, win 115, options [nop,nop,TS val 146111 ecr 398850], length 44 21:14:51.762710 IP corvina.vineyard.sikkerhed.org.sunrpc > malbec.vineyard.sikkerhed.org.948: Flags [.], ack 45, win 114, options [nop,nop,TS val 398850 ecr 146111], length 0 21:14:51.763282 IP corvina.vineyard.sikkerhed.org.sunrpc > malbec.vineyard.sikkerhed.org.948: Flags [P.], seq 1:473, ack 45, win 114, options [nop,nop,TS val 398850 ecr 146111], length 472 21:14:51.763302 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [.], ack 473, win 123, options [nop,nop,TS val 146111 ecr 398850], length 0 21:14:51.764059 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [F.], seq 45, ack 473, win 123, options [nop,nop,TS val 146111 ecr 398850], length 0 21:14:51.764454 IP corvina.vineyard.sikkerhed.org.sunrpc > malbec.vineyard.sikkerhed.org.948: Flags [F.], seq 473, ack 46, win 114, options [nop,nop,TS val 398850 ecr 146111], length 0 21:14:51.764478 IP malbec.vineyard.sikkerhed.org.948 > corvina.vineyard.sikkerhed.org.sunrpc: Flags [.], ack 474, win 123, options [nop,nop,TS val 146111 ecr 398850], length 0 The following is output from tcpdump on malbec while runing this command: ~ # time mount.nfs4 10.0.0.51:/ /mnt -o soft,intr,timeo=10 21:14:58.397327 IP malbec.vineyard.sikkerhed.org.872 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1298959870, win 14600, options [mss 1460,sackOK,TS val 147769 ecr 0,nop,wscale 7], length 0 21:14:58.397655 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.872: Flags [R.], seq 0, ack 1298959871, win 0, length 0 21:14:59.470270 IP malbec.vineyard.sikkerhed.org.854 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 4111013041, win 14600, options [mss 1460,sackOK,TS val 148038 ecr 0,nop,wscale 7], length 0 21:14:59.470569 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.854: Flags [R.], seq 0, ack 4111013042, win 0, length 0 21:15:01.506179 IP malbec.vineyard.sikkerhed.org.988 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1642454567, win 14600, options [mss 1460,sackOK,TS val 148547 ecr 0,nop,wscale 7], length 0 21:15:01.506514 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.988: Flags [R.], seq 0, ack 1642454568, win 0, length 0 21:15:05.542216 IP malbec.vineyard.sikkerhed.org.882 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 3844460520, win 14600, options [mss 1460,sackOK,TS val 149556 ecr 0,nop,wscale 7], length 0 21:15:05.542484 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.882: Flags [R.], seq 0, ack 3844460521, win 0, length 0 21:15:13.602228 IP malbec.vineyard.sikkerhed.org.969 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1317773588, win 14600, options [mss 1460,sackOK,TS val 151571 ecr 0,nop,wscale 7], length 0 21:15:13.602527 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.969: Flags [R.], seq 0, ack 1317773589, win 0, length 0 21:15:18.615027 ARP, Request who-has malbec.vineyard.sikkerhed.org tell corvina.vineyard.sikkerhed.org, length 46 21:15:18.615048 ARP, Reply malbec.vineyard.sikkerhed.org is-at cc:52:af:46:af:23 (oui Unknown), length 28 21:15:23.622223 IP malbec.vineyard.sikkerhed.org.1003 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 2896563167, win 14600, options [mss 1460,sackOK,TS val 154076 ecr 0,nop,wscale 7], length 0 21:15:23.622557 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.1003: Flags [R.], seq 0, ack 2896563168, win 0, length 0 21:15:28.629913 ARP, Request who-has corvina.vineyard.sikkerhed.org tell malbec.vineyard.sikkerhed.org, length 28 21:15:28.630223 ARP, Reply corvina.vineyard.sikkerhed.org is-at 00:9c:02:ab:db:54 (oui Unknown), length 46 21:15:33.662200 IP malbec.vineyard.sikkerhed.org.727 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1334644196, win 14600, options [mss 1460,sackOK,TS val 156586 ecr 0,nop,wscale 7], length 0 21:15:33.663657 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.727: Flags [R.], seq 0, ack 1334644197, win 0, length 0 21:15:43.698207 IP malbec.vineyard.sikkerhed.org.rsync > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 688828331, win 14600, options [mss 1460,sackOK,TS val 159095 ecr 0,nop,wscale 7], length 0 21:15:43.698541 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.rsync: Flags [R.], seq 0, ack 688828332, win 0, length 0 21:15:48.707710 ARP, Request who-has malbec.vineyard.sikkerhed.org tell corvina.vineyard.sikkerhed.org, length 46 21:15:48.707726 ARP, Reply malbec.vineyard.sikkerhed.org is-at cc:52:af:46:af:23 (oui Unknown), length 28 21:15:53.738188 IP malbec.vineyard.sikkerhed.org.946 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 2021272456, win 14600, options [mss 1460,sackOK,TS val 161605 ecr 0,nop,wscale 7], length 0 21:15:53.738519 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.946: Flags [R.], seq 0, ack 2021272457, win 0, length 0 21:16:03.806216 IP malbec.vineyard.sikkerhed.org.902 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 3889059201, win 14600, options [mss 1460,sackOK,TS val 164122 ecr 0,nop,wscale 7], length 0 21:16:03.806546 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.902: Flags [R.], seq 0, ack 3889059202, win 0, length 0 21:16:08.821900 ARP, Request who-has corvina.vineyard.sikkerhed.org tell malbec.vineyard.sikkerhed.org, length 28 21:16:08.822172 ARP, Reply corvina.vineyard.sikkerhed.org is-at 00:9c:02:ab:db:54 (oui Unknown), length 46 21:16:13.874209 IP malbec.vineyard.sikkerhed.org.712 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1480927452, win 14600, options [mss 1460,sackOK,TS val 166639 ecr 0,nop,wscale 7], length 0 21:16:13.874553 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.712: Flags [R.], seq 0, ack 1961062188, win 0, length 0 21:16:18.880588 ARP, Request who-has malbec.vineyard.sikkerhed.org tell corvina.vineyard.sikkerhed.org, length 46 21:16:18.880605 ARP, Reply malbec.vineyard.sikkerhed.org is-at cc:52:af:46:af:23 (oui Unknown), length 28 21:16:23.910209 IP malbec.vineyard.sikkerhed.org.758 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1375860626, win 14600, options [mss 1460,sackOK,TS val 169148 ecr 0,nop,wscale 7], length 0 21:16:23.910532 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.758: Flags [R.], seq 0, ack 1375860627, win 0, length 0 21:16:33.982258 IP malbec.vineyard.sikkerhed.org.694 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 1769203987, win 14600, options [mss 1460,sackOK,TS val 171666 ecr 0,nop,wscale 7], length 0 21:16:33.982579 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.694: Flags [R.], seq 0, ack 1769203988, win 0, length 0 21:16:44.026241 IP malbec.vineyard.sikkerhed.org.841 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 530553783, win 14600, options [mss 1460,sackOK,TS val 174177 ecr 0,nop,wscale 7], length 0 21:16:44.026505 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.841: Flags [R.], seq 0, ack 530553784, win 0, length 0 21:16:46.213388 IP malbec.vineyard.sikkerhed.org.43460 > corvina.vineyard.sikkerhed.org.ssh: Flags [P.], seq 64:128, ack 33, win 325, options [nop,nop,TS val 174723 ecr 397437], length 64 21:16:46.213859 IP corvina.vineyard.sikkerhed.org.ssh > malbec.vineyard.sikkerhed.org.43460: Flags [P.], seq 33:65, ack 128, win 199, options [nop,nop,TS val 427466 ecr 174723], length 32 21:16:46.213883 IP malbec.vineyard.sikkerhed.org.43460 > corvina.vineyard.sikkerhed.org.ssh: Flags [.], ack 65, win 325, options [nop,nop,TS val 174723 ecr 427466], length 0 21:16:54.094242 IP malbec.vineyard.sikkerhed.org.kerberos-master > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 2673083337, win 14600, options [mss 1460,sackOK,TS val 176694 ecr 0,nop,wscale 7], length 0 21:16:54.094568 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.kerberos-master: Flags [R.], seq 0, ack 2673083338, win 0, length 0 21:17:04.134227 IP malbec.vineyard.sikkerhed.org.1019 > corvina.vineyard.sikkerhed.org.nfs: Flags [S], seq 2176607713, win 14600, options [mss 1460,sackOK,TS val 179204 ecr 0,nop,wscale 7], length 0 21:17:04.134566 IP corvina.vineyard.sikkerhed.org.nfs > malbec.vineyard.sikkerhed.org.1019: Flags [R.], seq 0, ack 2176607714, win 0, length 0 21:18:46.314021 IP malbec.vineyard.sikkerhed.org.43460 > corvina.vineyard.sikkerhed.org.ssh: Flags [P.], seq 128:192, ack 65, win 325, options [nop,nop,TS val 204749 ecr 427466], length 64 21:18:46.314462 IP corvina.vineyard.sikkerhed.org.ssh > malbec.vineyard.sikkerhed.org.43460: Flags [P.], seq 65:97, ack 192, win 199, options [nop,nop,TS val 457494 ecr 204749], length 32 21:18:46.314482 IP malbec.vineyard.sikkerhed.org.43460 > corvina.vineyard.sikkerhed.org.ssh: Flags [.], ack 97, win 325, options [nop,nop,TS val 204749 ecr 457494], length 0 21:18:51.317908 ARP, Request who-has corvina.vineyard.sikkerhed.org tell malbec.vineyard.sikkerhed.org, length 28 21:18:51.318177 ARP, Reply corvina.vineyard.sikkerhed.org is-at 00:9c:02:ab:db:54 (oui Unknown), length 46 mount command outputs mount.nfs4: Connection timed out mount.nfs4 10.0.0.51:/ /mnt -o soft,intr,timeo=10 0,00s user 0,00s system 0% cpu 2:05,80 total Returncode is 32 Server configuration I have enabled idmapd by adding NEED_IDMAPD=yes in /etc/default/nfs-common. Bind mounts in /etc/fstab: # nfs-audio /data/audio /exports/audio none bind 0 0 # nfs-clear /data/clear /exports/clear none bind 0 0 # nfs-video /data/video /exports/video none bind 0 0 /etc/exports: /exports 10.0.0.0/255.255.255.0(rw,no_root_squash,no_subtree_check,fsid=0,crossmnt) /exports/video 10.0.0.0/255.255.255.0(rw,no_root_squash,no_subtree_check,crossmnt) Output from # ls -al /exports total 20 drwxr-xr-x 5 root root 4096 Jul 2 14:14 ./ drwxr-xr-x 28 root root 4096 Jul 2 13:46 ../ drwxr-xr-x 7 tdn audio 4096 Jun 7 11:30 audio/ drwxr-xr-x 11 root root 4096 Jun 29 12:07 clear/ drwxrwx--- 12 tdn video 4096 Jun 7 09:46 video/

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• Why would a server not send a SYN/ACK packet in response to a SYN packet

  - by codemonkey

  Lately, we've become aware of a TCP connection issue that is mostly limited to mac and Linux users who browse our websites. From the user perspective, it presents itself as a really long connection time to our websites (11 seconds). We've managed to track down the technical signature of this problem, but can't figure out why it is happening or how to fix it. Basically, what is happening is that the client's machine is sending the SYN packet to establish the TCP connection and the web server receives it, but does not respond with the SYN/ACK packet. After the client has sent many SYN packets, the server finally responds with a SYN/ACK packet and everything is fine for the remainder of the connection. And, of course, the kicker to the problem: it is intermittent and does not happen all the time (though it does happen between 10-30% of the time) We are using Fedora 12 Linux as the OS and Nginx as the web server.

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• Server not sending a SYN/ACK packet in response to a SYN packet

  - by jeff

  Using iptraf, tcpdump and wireshark I can see a SYN packet coming in but only the ACK FLAG is set in reply packet. I'm running Debian 5 with kernel 2.6.36 I've turned off window_scaling and tcp_timestamps, tcp_tw_recycle and tcp_tw_reuse: cat /etc/sysctl.conf net.ipv4.tcp_tw_recycle = 0 net.ipv4.tcp_tw_reuse = 0 net.ipv4.tcp_window_scaling = 0 net.ipv4.tcp_timestamps = 0 I've attached an image of the wireshark output. http://imgur.com/pECG0.png Output to netstat netstat -natu | grep '72.23.130.104' tcp 0 0 97.107.134.212:18000 72.23.130.104:42905 SYN_RECV I've been doing everything possible to find a solution and have yet to figure out the problem, so any help/suggestions are much appreciated. UPDATE 1: I've set tcp_syncookies = 0 and noticed I am now replying with 1 SYN+ACK for every 50 SYN requests. The host trying to connect is sending a SYN request about once every second. PCAP FILE

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• Linux, some packets are not being NAT

  - by user70932

  Hi, I'm trying to NAT HTTP traffic, I'm new to this and facing some issues. What i'm trying to do is NAT client HTTP requests to a webserver. CLIENT - NAT BOX - WEBSERVER When the client open the IP of the NAT BOX, the request should be pass to the web server. But I'm getting "HTTP request sent, awaiting response..." and then wait serveral minutes before the request is done. Looking at the tcpdump output, it looks like the first Syn packet on (10:48:54) is being NAT but not the second, third, fourth... ACK or PSH packets, and wait until (10:52:04) it starts NAT again on the ACK packet. The iptables command I'm using is: iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 80 \ -j DNAT --to-destination WEBSERVER I'm wondering what could have caused this behavior? Thanks alot. 10:48:54.907861 IP (tos 0x0, ttl 49, id 16395, offset 0, flags [DF], proto: TCP (6), length: 48) CLIENT.61736 > NATBOX.http: S, cksum 0x6019 (correct), 1589600740:1589600740(0) win 5840 <mss 1460,nop,wscale 8> 10:48:54.907874 IP (tos 0x0, ttl 48, id 16395, offset 0, flags [DF], proto: TCP (6), length: 48) CLIENT.61736 > WEBSERVER.http: S, cksum 0xb5d7 (correct), 1589600740:1589600740(0) win 5840 <mss 1460,nop,wscale 8> 10:48:55.102696 IP (tos 0x0, ttl 49, id 16397, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x2727 (correct), ack 2950613896 win 23 10:48:55.102963 IP (tos 0x0, ttl 49, id 16399, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:48:58.103078 IP (tos 0x0, ttl 49, id 16401, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:48:58.366344 IP (tos 0x0, ttl 49, id 16403, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:04.103204 IP (tos 0x0, ttl 49, id 16405, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:04.363943 IP (tos 0x0, ttl 49, id 16407, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:16.101583 IP (tos 0x0, ttl 49, id 16409, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:16.363475 IP (tos 0x0, ttl 49, id 16411, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:40.100796 IP (tos 0x0, ttl 49, id 16413, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:40.563898 IP (tos 0x0, ttl 49, id 16415, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:50:28.099396 IP (tos 0x0, ttl 49, id 16417, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:50:28.761678 IP (tos 0x0, ttl 49, id 16419, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:52:04.093668 IP (tos 0x0, ttl 49, id 16421, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:52:04.093678 IP (tos 0x0, ttl 48, id 16421, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > WEBSERVER.http: P 1589600741:1589600861(120) ack 2950613896 win 23 10:52:04.291021 IP (tos 0x0, ttl 49, id 16423, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x25d3 (correct), ack 217 win 27 10:52:04.291028 IP (tos 0x0, ttl 48, id 16423, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7b91 (correct), ack 217 win 27 10:52:04.300708 IP (tos 0x0, ttl 49, id 16425, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x253c (correct), ack 368 win 27 10:52:04.300714 IP (tos 0x0, ttl 48, id 16425, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7afa (correct), ack 368 win 27 10:52:04.301417 IP (tos 0x0, ttl 49, id 16427, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: F, cksum 0x253b (correct), 120:120(0) ack 368 win 27 10:52:04.301438 IP (tos 0x0, ttl 48, id 16427, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: F, cksum 0x7af9 (correct), 120:120(0) ack 368 win 27 10:52:04.498875 IP (tos 0x0, ttl 49, id 16429, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x253a (correct), ack 369 win 27 10:52:04.498881 IP (tos 0x0, ttl 48, id 16429, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7af8 (correct), ack 369 win 27

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• Millions of SYN_RECV connections, no DDoS

  - by ThomK

  We have such server structure: reverse proxy (nginx) - worker (uwsgi) - postgresql / memcached. All servers are in local network behind router, with NATed external ip:ports (http/s 80/443 to proxy, and ssh 22 to all servers). Problem is, that sometimes proxy server netstat reports MILLIONS of SYN_RECV connections. From same IP / same ports. Like that: nginx ~ # netstat -n | grep 83.238.153.195 tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV [...] And this is not DDoS, because all IPs affected belongs to our website users. On side note, users says that it's not affecting them. Website is online and working, but... that particular one (from example above) told me that website is down and Firefox can't connect. I've done tcpdump. 19:42:14.826011 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:14.826042 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:17.887331 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:17.887343 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:19.065497 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:23.918064 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:23.918076 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:25.265499 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.265501 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.758051 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:37.758069 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:40.714360 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:40.714374 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:41.665503 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:46.751073 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:46.751087 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:47.665498 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:59.865499 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:01.265500 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:13.320382 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:13.320399 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:16.320556 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:16.320569 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:17.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:22.250069 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:22.250080 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.665500 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.865501 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:35.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:37.903038 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:37.903054 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:40.772899 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:40.772912 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:41.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:46.793057 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:46.793069 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:47.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:49.465503 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 Anyone have some thoughts on that?

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• server will not reply (syn -ack)

  - by Brent

  I like to use the following commands to manage 'TIME_WAIT', in the hope to free up resources. echo 20 > /proc/sys/net/ipv4/tcp_fin_timeout sysctl -w net.ipv4.tcp_tw_reuse=1 sysctl -w net.ipv4.tcp_tw_recycle=1 I found something interesting while doing a tcpdump. Sometimes if a client makes a connection (syn), the server will not reply (syn -ack). My question is, could it be because of the top three commands.

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• using tcpdump to display XML API requests without headers or ack packets

  - by Carmageddon

  I need assistance, I am trying to use tcpdump in order to capture API requests and responses between two servers, so far I have the following command: tcpdump -iany -tpnAXs0 host xxx.xxx.xxx.xxx and port 6666 My problem is, that the output is still hard to read, because it sends the Headers, and the ack packets. I would like to remove those and only see the XML bodies. I tried to use grep -v, but apparently this is all one request, so it filters the entire thing... Thanks!

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• How to use ack to search for file name

  - by dorelal

  I have started using ack which is much faster than grep. However using ack I want to search for file name rather than file contents. Is there a way to do that?

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• LDAP over SSL with an EFI Fiery printer

  - by austinian

  I've got a printer with a Fiery running 8e Release 2. I can authenticate users against AD using the LDAP configuration, but I can only get it to work if I don't use SSL/TLS, and only if I use SIMPLE authentication. Right now, it's authenticating using a fairly low-impact user, but it's also the only system on our network that's not using LDAPS. I can get AD info fine over LDAPS using ldp.exe from my machine, our firewall, our mail filter, our linux boxes, etc. The only problem child is the Fiery. I've added the LDAP server certificate as a trusted cert to the Fiery, but after I check the box for Secure Communication and change the port to 636, pressing Validate results in a dialog box coming up saying: LDAP Validation Failed Server Name invalid or server is unavailable. I've tried changing the server name to use just the name, the FQDN, and the IP address, and changed it to another server, just to see if it was just this AD server that was fussy with the Fiery. EDIT: removed LDP output, added packet capture analysis from wireshark: The conversation seems pretty normal to me, up to the point where the Fiery terminates the connection after the server sends back a handshake response. Maybe they messed up their TLS implementation? I'm trying support, but it's been fairly useless so far. The cert is a SHA-2 (sha256RSA) 2048-bit certificate. Also, it looks like the Fiery is specifying TLS 1.0. Looking at http://msdn.microsoft.com/en-us/library/windows/desktop/aa374757(v=vs.85).aspx, I'm not seeing SHA256 and TLS 1.0 combination being supported by SChannel. headdesk perhaps that's why, after the DC changes the cipher spec, the connection is terminated by the Fiery? TLS 1.1 and 1.2 are enabled on the DC. Wireshark conversation: DC: 172.17.2.22, Fiery: 172.17.2.42 No. Time Source Source Port Destination Destination Port Protocol Length Info 1 0.000000000 172.17.2.42 48633 172.17.2.22 ldaps TCP 74 48633 > ldaps [SYN] Seq=0 Win=5840 Len=0 MSS=1460 SACK_PERM=1 TSval=3101761 TSecr=0 WS=4 2 0.000182000 Dell_5e:94:e3 Broadcast ARP 60 Who has 172.17.2.42? Tell 172.17.2.22 3 0.000369000 TyanComp_c9:0f:90 Dell_5e:94:e3 ARP 60 172.17.2.42 is at 00:e0:81:c9:0f:90 4 0.000370000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 74 ldaps > 48633 [SYN, ACK] Seq=0 Ack=1 Win=8192 Len=0 MSS=1460 WS=256 SACK_PERM=1 TSval=67970573 TSecr=3101761 5 0.000548000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [ACK] Seq=1 Ack=1 Win=5840 Len=0 TSval=3101761 TSecr=67970573 6 0.001000000 172.17.2.42 48633 172.17.2.22 ldaps TLSv1 147 Client Hello 7 0.001326000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 1514 [TCP segment of a reassembled PDU] 8 0.001513000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 1514 [TCP segment of a reassembled PDU] 9 0.001515000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [ACK] Seq=82 Ack=1449 Win=8736 Len=0 TSval=3101761 TSecr=67970573 10 0.001516000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [ACK] Seq=82 Ack=2897 Win=11632 Len=0 TSval=3101761 TSecr=67970573 11 0.001732000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 1514 [TCP segment of a reassembled PDU] 12 0.001737000 172.17.2.22 ldaps 172.17.2.42 48633 TLSv1 1243 Server Hello, Certificate, Certificate Request, Server Hello Done 13 0.001738000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [ACK] Seq=82 Ack=4345 Win=14528 Len=0 TSval=3101761 TSecr=67970573 14 0.001739000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [ACK] Seq=82 Ack=5522 Win=17424 Len=0 TSval=3101761 TSecr=67970573 15 0.002906000 172.17.2.42 48633 172.17.2.22 ldaps TLSv1 78 Certificate 16 0.004155000 172.17.2.42 48633 172.17.2.22 ldaps TLSv1 333 Client Key Exchange 17 0.004338000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 66 ldaps > 48633 [ACK] Seq=5522 Ack=361 Win=66304 Len=0 TSval=67970573 TSecr=3101762 18 0.004338000 172.17.2.42 48633 172.17.2.22 ldaps TLSv1 72 Change Cipher Spec 19 0.005481000 172.17.2.42 48633 172.17.2.22 ldaps TLSv1 327 Encrypted Handshake Message 20 0.005645000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 66 ldaps > 48633 [ACK] Seq=5522 Ack=628 Win=66048 Len=0 TSval=67970574 TSecr=3101762 21 0.010247000 172.17.2.22 ldaps 172.17.2.42 48633 TLSv1 125 Change Cipher Spec, Encrypted Handshake Message 22 0.016451000 172.17.2.42 48633 172.17.2.22 ldaps TCP 66 48633 > ldaps [FIN, ACK] Seq=628 Ack=5581 Win=17424 Len=0 TSval=3101765 TSecr=67970574 23 0.016630000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 66 ldaps > 48633 [ACK] Seq=5581 Ack=629 Win=66048 Len=0 TSval=67970575 TSecr=3101765 24 0.016811000 172.17.2.22 ldaps 172.17.2.42 48633 TCP 60 ldaps > 48633 [RST, ACK] Seq=5581 Ack=629 Win=0 Len=0

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• Webserver Responses Hanging

  - by drscroogemcduck

  From some networks requesting certain images on our webserver is very flakey. I've looked at tcpdumps on both sides and the server sends back part of the file and the client ACKs the TCP packet but the server never receives the ACK. The servers view: 41 19.941136 212.169.34.114 209.20.73.85 TCP 52456 > http [SYN] Seq=0 Win=8192 Len=0 MSS=1460 WS=2 42 19.941136 209.20.73.85 212.169.34.114 TCP http > 52456 [SYN, ACK] Seq=0 Ack=1 Win=5440 Len=0 MSS=1360 46 20.041142 212.169.34.114 209.20.73.85 TCP 52456 > http [ACK] Seq=1 Ack=1 Win=65280 Len=0 47 20.045142 212.169.34.114 209.20.73.85 HTTP GET /map/map/s+74-WBkWk0aR28Yy-YjXA== HTTP/1.1 48 20.045142 209.20.73.85 212.169.34.114 TCP http > 52456 [ACK] Seq=1 Ack=522 Win=6432 Len=0 49 20.045142 209.20.73.85 212.169.34.114 TCP [TCP segment of a reassembled PDU] (Part of the content of the image 2720 bytes. i assume it is reassembled in tcpdump and it is fragmented over the wire.) ** never receives the ACK sent in frame 282 and will eventually resend the tcp segment ** The clients view: 274 26.161773 10.0.16.67 209.20.73.85 TCP 52456 > http [SYN] Seq=0 Win=8192 Len=0 MSS=1460 WS=2 276 26.262867 209.20.73.85 10.0.16.67 TCP http > 52456 [SYN, ACK] Seq=0 Ack=1 Win=5440 Len=0 MSS=1360 277 26.263255 10.0.16.67 209.20.73.85 TCP 52456 > http [ACK] Seq=1 Ack=1 Win=65280 Len=0 278 26.265193 10.0.16.67 209.20.73.85 HTTP GET /map/map/s+74-WBkWk0aR28Yy-YjXA== HTTP/1.1 279 26.365562 209.20.73.85 10.0.16.67 TCP http > 52456 [ACK] Seq=1 Ack=522 Win=6432 Len=0 280 26.368002 209.20.73.85 10.0.16.67 TCP [TCP segment of a reassembled PDU] (Part of the content of the image. Only 1400 bytes.) 282 26.571380 10.0.16.67 209.20.73.85 TCP 52456 > http [ACK] Seq=522 Ack=1361 Win=65280 Len=0 The network we are having trouble with is NATd. Is there any kind of explanation for this weirdness?

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• SYN receives RST,ACK very frequently

  - by user1289508

  Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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• TCP stops sending weirdly.

  - by Utoah

  In case to find out the cause of TCP retransmits on my Linux (RHEL, kernel 2.6.18) servers connecting to the same switch. I had a client-server pair send "Hello" to each other every 200us and captured the packets with tcpdump on the client machine. The command I used to mimic client and server are: while [ 0 ]; do echo "Hello"; usleep 200; done | nc server 18510 while [ 0 ]; do echo "Hello"; usleep 200; done | nc -l 18510 When the server machine was busy serving some other requests, the client suffered from abrupt retransmits occasionally. But the output of tcpdump seemed irrational. 16:04:58.898970 IP server.18510 > client.34533: P 4531:4537(6) ack 3204 win 123 <nop,nop,timestamp 1923778643 3452833828> 16:04:58.901797 IP client.34533 > server.18510: P 3204:3210(6) ack 4537 win 33 <nop,nop,timestamp 3452833831 1923778643> 16:04:58.901855 IP server.18510 > client.34533: P 4537:4549(12) ack 3210 win 123 <nop,nop,timestamp 1923778646 3452833831> 16:04:58.903871 IP client.34533 > server.18510: P 3210:3216(6) ack 4549 win 33 <nop,nop,timestamp 3452833833 1923778646> 16:04:58.903950 IP server.18510 > client.34533: P 4549:4555(6) ack 3216 win 123 <nop,nop,timestamp 1923778648 3452833833> 16:04:58.905796 IP client.34533 > server.18510: P 3216:3222(6) ack 4555 win 33 <nop,nop,timestamp 3452833835 1923778648> 16:04:58.905860 IP server.18510 > client.34533: P 4555:4561(6) ack 3222 win 123 <nop,nop,timestamp 1923778650 3452833835> 16:04:58.908903 IP client.34533 > server.18510: P 3222:3228(6) ack 4561 win 33 <nop,nop,timestamp 3452833838 1923778650> 16:04:58.908966 IP server.18510 > client.34533: P 4561:4567(6) ack 3228 win 123 <nop,nop,timestamp 1923778653 3452833838> 16:04:58.911855 IP client.34533 > server.18510: P 3228:3234(6) ack 4567 win 33 <nop,nop,timestamp 3452833841 1923778653> 16:04:59.112573 IP client.34533 > server.18510: P 3228:3234(6) ack 4567 win 33 <nop,nop,timestamp 3452834042 1923778653> 16:04:59.112648 IP server.18510 > client.34533: P 4567:5161(594) ack 3234 win 123 <nop,nop,timestamp 1923778857 3452834042> 16:04:59.112659 IP client.34533 > server.18510: P 3234:3672(438) ack 5161 win 35 <nop,nop,timestamp 3452834042 1923778857> 16:04:59.114427 IP server.18510 > client.34533: P 5161:5167(6) ack 3672 win 126 <nop,nop,timestamp 1923778858 3452834042> 16:04:59.114439 IP client.34533 > server.18510: P 3672:3678(6) ack 5167 win 35 <nop,nop,timestamp 3452834044 1923778858> 16:04:59.116435 IP server.18510 > client.34533: P 5167:5173(6) ack 3678 win 126 <nop,nop,timestamp 1923778860 3452834044> 16:04:59.116444 IP client.34533 > server.18510: P 3678:3684(6) ack 5173 win 35 <nop,nop,timestamp 3452834046 1923778860> Packet 3228:3234(6) from client was retransmitted due to ack timeout. What I could not understand was that the client machine did not send out any packets after the first 3228:3234(6) packets was sent. The server machine had advertised a window (scaled) large enough. The data transfer up to the retransmit was fine which meant no slow start should be in action. What can cause the client machine to stop sending until the packet timed out? BTW, I am unable to run tcpdump on the server machine.

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• Is there a tool to do round trip software engineering between a sequence diagram and a group of objects that message back and forth?

  - by DeveloperDon

  Is there a tool to do round trip software engineering between a sequence diagram and a group of objects that message back and forth? Perhaps this seems a little exotic, but it seems like a function that includes message calls or even method invocations on other objects could be automatically converted to a sequence diagram given that it is not hard to do manually. Similarly, when a sequence diagram is modified, based on the message name and type of message, should it not be possible to add a message or method to the calling object?

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• How to create HL7 ACK messages in c# by nhapi

  - by Seraj

  Dear, I have created a HL& response message(ADR_19), by using nHAPI in c#. Please tell me how to add ACK message in response HL message Thanks for your Kind Cooperation

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• checksum error with building an HTTP packet(but over TCP, like syn/ack its ok)

  - by Hila

  I am building a NAT program,I change each packet that comes from our internal subnet, change it's source IP address by libnet functions.( catch the packet with libpcap, put it sniff structures and build the new packet with libnet) I am trying to build an http packet. When I look on wireshark, I see that the new packet that I have built is exectly like the original packet(the only diffrent is that I changed the src port and ip), but there is a checksum error, So the server don't do anything with the packet that I have sent to him, beacuse the cheksum field is wrong. When I send a tcp packet(like syn or ack), the checksum is ok, and the server respons. Is anyone knows what can cause this problem? the new checksum in other packets is calculated as it should be.. but in the HTTP packet it doesn't..

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• Best grep-like tool

  - by e-satis

  I do in file search a lot, and used to love grep. Then I learn the existence of egrep, so I switched to benefit from the advanced regexp. Then I discovered the Eclipse search tool. Much easier to use that grep. Then I found ack : fast, easy, powerful. And now I use grin, which is smooth for pythonistas. I know there is also a couple of this kind of tools with a GUI. So what tool do you use, and why do you think it's the best. Practical features generally are : fast to fire and use; speedy processing; automatically ignore useless files; colored output; output lines, filename, context; allow complex regexp; allow a custom filtering and ouput; GUI + command line intergation; let you open an editor from the result set. There are some related posts on SO : http://stackoverflow.com/questions/87350/what-are-good-grep-tool-for-windows http://stackoverflow.com/questions/981601/colorized-grep-viewing-the-entire-file-with-highlighting http://stackoverflow.com/questions/1028107/is-there-some-unix-util-that-will-allow-me-to-grep-multiple-files-with-little-type http://stackoverflow.com/questions/1027906/unix-find-grep-syntax-vs-awk

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• What would cause my SendMail server not to acknowledge receiving a TCP Sequence?

  - by Mike B

  My TCP/IP Stack knowledge is a little rusty so please bear with me.... I have a CentOS 5.7 server with SendMail and am having seeing intermittent timeout issues sending email (particularly larger email) to other remote domains. It doesn't happen with all attachments or recipient domains. Just some. After some extended troubleshooting, I think I've narrowed it down to TCP Sequences not being acknowledged. Here's a breakdown of the TCP session from a packet capture I collected directly on my MTA (fooMTA): Packet 1 - 11: Standard TCP handshake followed by initial SMTP conversation. No errors. Packet #12 Recipient MTA: TCP sequence 231. Ack 91. Packet #13 FooMTA: TCP sequence 91. Ack 305. Packet #14 FooMTA: TCP sequence 1115. Ack 305. Packet #15 Recipient MTA: TCP sequence 305. Ack 2495. Packet #16 FooMTA: TCP sequence 2495. Ack 305. Packet #17 FooMTA: TCP sequence 5255. Ack 305. Packet #18: Recipient MTA: TCP sequence 305. Ack 5255. Packet #19: FooMTA: TCP sequence 6635. Ack 305. Packet #20: FooMTA: TCP sequence 8015. Ack 305. Packet #21: Recipient MTA: TCP Sequence 305. Ack 8015. Packet #22: FooMTA: TCP Sequence 10775. Ack 305. Packet #23: FooMTA: TCP Sequence 13535. Ack 305. Packet #24: Recipient MTA: TCP sequence 305. Ack 10775 Packet #25: FooMTA: TCP Sequence 14915. Ack 305 It keeps going like this with my server still thinking it hasn’t received sequence 305… in response the remote side eventually retransmits its prior data thinking that it never arrived. Eventually the gap gets so large that no new data is sent and the remote MTA keeps retransmitting old stuff. This contributes to an exponential backoff and eventually the remote side gives up. What’s strange to me is that I see the “missing” TCP sequence (305 in this case) arriving back to my server (via a packet capture collected directly from fooMTA) So I don’t get why my server keeps asking for it. Could this be firewall related? What would be the next step in troubleshooting?

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• How to get http requests details in a tcpdump?

  - by tucson

  I am trying to get a tcpdump trace of some http requests. Here is what I got so far (I replaced the real IP addresses with REMOTE and LOCAL): C:\>Windump -na -i 3 ip host REMOTE and ip src LOCAL and tcp port 80 Windump: listening on \Device\NPF_{8056BE5E-BDBB-44E6-B492-9274B410AD66} 13:13:34.985460 IP LOCAL.4261 > REMOTE.80: . 1784894764:1784894765(1) ack 1268208398 win 65535 13:13:38.589175 IP LOCAL.4302 > REMOTE.80: F 3708464308:3708464308(0) ack 982485614 win 65535 13:13:38.589285 IP LOCAL.4303 > REMOTE.80: F 890175362:890175362(0) ack 2462862919 win 65535 13:13:38.589330 IP LOCAL.4304 > REMOTE.80: F 1838079178:1838079178(0) ack 156173959 win 65535 13:13:38.589374 IP LOCAL.4305 > REMOTE.80: F 3952718843:3952718843(0) ack 2209231545 win 65535 13:13:38.589413 IP LOCAL.4306 > REMOTE.80: F 446105750:446105750(0) ack 3141849979 win 65535 13:13:38.590265 IP LOCAL.4302 > REMOTE.80: . ack 2 win 65535 13:13:38.590403 IP LOCAL.4304 > REMOTE.80: . ack 2 win 65535 13:13:38.590429 IP LOCAL.4303 > REMOTE.80: . ack 2 win 65535 13:13:38.590484 IP LOCAL.4305 > REMOTE.80: . ack 2 win 65535 13:13:38.590514 IP LOCAL.4306 > REMOTE.80: . ack 2 win 65535 But I do not get the following level of details: Request URL:http://domain.com/index.php Request Method:POST Status Code:200 OK POST /index.php HTTP/1.1 Host: domain.com Connection: keep-alive Content-Length: 151 Cache-Control: max-age=0 etc How can I get this level of data?

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