{"id":33,"date":"2017-03-02T08:41:15","date_gmt":"2017-03-02T08:41:15","guid":{"rendered":"http:\/\/www.web-workers.ch\/?p=33"},"modified":"2017-06-23T07:09:18","modified_gmt":"2017-06-23T07:09:18","slug":"how-to-capture-tcp-retransmissions-on-linux","status":"publish","type":"post","link":"https:\/\/www.web-workers.ch\/index.php\/2017\/03\/02\/how-to-capture-tcp-retransmissions-on-linux\/","title":{"rendered":"How to capture TCP retransmissions on Linux"},"content":{"rendered":"

You are probably experiencing perfomance issues during file transfers on a Linux box and you would like to find out if there are some network issues recognized. \u00a0First you may want to find out if there are a\u00a0lot of re-transmissions during transfers.<\/p>\n

Produce Data<\/h1>\n

Write data to the destination you experience performance issues with, create a small script for that. You may want to use java jcifs to transfer files. See below an example of jcifs_copy.sh<\/p>\n

#!\/bin\/bash
\n<\/span> COUNTERSTART=1<\/span><\/span>
\n COUNTEREND=50<\/span>
\n TARGET=\/\/storso11\/nas1001<\/span>
\n USERNAME=user<\/span>
\n PASSWORD=pass<\/span>
\n FILE=\/\/opt\/sybase\/12.5.4\/ASE-12_5\/bin\/dataserver<\/span>
\n LOGFILE=\/logs\/$(basename $0)<\/span><\/p>\n

date > ${LOGFILE}
\n<\/span>
\n while [\u00a0 ${COUNTERSTART} -le ${COUNTEREND} ]; do<\/span>
\n \u00a0\u00a0echo Run: ${COUNTERSTART}<\/span><\/span>
\n \u00a0\u00a0java -Djcifs.smb.client.useExtendedSecurity=0 -Djcifs.smb.lmCompatibility=0 -cp \/local\/flamingo\/lib\/ext\/jcifs.jar NasWriteTest smb:${TARGET} ${USERNAME} ${PASSWORD} ${FILE} >> ${LOGFILE}<\/span>
\n \u00a0 let COUNTERSTART<\/span>=${COUNTERSTART}<\/span>+1<\/span>
\n \u00a0 sleep 5<\/span>
\n done<\/span><\/p><\/blockquote>\n

In case you have mounted a network share, you may want to use the dd command (press CTRL-C to abort and to see the results) to generate data.<\/p>\n

# dd if=\/dev\/urandom of=testfileR bs=8k count=10000; sync;
\n<\/code> # dd if=\/dev\/urandom of=testfileR bs=8k count=10000; sync;<\/code><\/p>\n

Capture ReTransmissions<\/h1>\n
\n

By using tshark<\/h3>\n

Hint: Make sure you have tshark installed, if you haven’t, install it by executing following command
\n# yum install wireshark
\n<\/code>Loaded plugins: fastestmirror, langpacks<\/code>Loading mirror speeds from cached hostfile<\/code> * base: mirror.switch.ch<\/code> * epel: mirror.23media.de<\/code> * extras: mirror.switch.ch<\/code> * updates: mirror.switch.ch<\/code>Resolving Dependencies<\/code>--> Running transaction check<\/code>---> Package wireshark.x86_64 0:1.10.14-10.el7 will be installed<\/code>--> Processing Dependency: libsmi.so.2()(64bit) for package: wireshark-1.10.14-10.el7.x86_64<\/code>--> Processing Dependency: libcares.so.2()(64bit) for package: wireshark-1.10.14-10.el7.x86_64<\/code>--> Running transaction check<\/code>---> Package c-ares.x86_64 0:1.10.0-3.el7 will be installed<\/code>---> Package libsmi.x86_64 0:0.4.8-13.el7 will be installed<\/code>--> Finished Dependency Resolution<\/code>Dependencies Resolved<\/code>=================================================================================================<\/code> Package Arch Version Repository Size<\/code>=================================================================================================<\/code>Installing:<\/code> wireshark x86_64 1.10.14-10.el7 base 13 M<\/code>Installing for dependencies:<\/code> c-ares x86_64 1.10.0-3.el7 base 78 k<\/code> libsmi x86_64 0.4.8-13.el7 base 2.3 M<\/code>Transaction Summary<\/code>=================================================================================================<\/code>Install 1 Package (+2 Dependent packages)<\/code>Total download size: 15 M<\/code>Installed size: 83 M<\/code>Is this ok [y\/d\/N]: y<\/code>Downloading packages:<\/code>(1\/3): c-ares-1.10.0-3.el7.x86_64.rpm | 78 kB 00:00:00<\/code>(2\/3): libsmi-0.4.8-13.el7.x86_64.rpm | 2.3 MB 00:00:01<\/code>(3\/3): wireshark-1.10.14-10.el7.x86_64.rpm | 13 MB 00:00:02<\/code>--------------------------------------------------------------------------------------------------------------------------------------------<\/code>Total 5.6 MB\/s | 15 MB 00:00:02<\/code>Running transaction check<\/code>Running transaction test<\/code>Transaction test succeeded<\/code>Running transaction<\/code> Installing : c-ares-1.10.0-3.el7.x86_64 1\/3<\/code> Installing : libsmi-0.4.8-13.el7.x86_64 2\/3<\/code> Installing : wireshark-1.10.14-10.el7.x86_64 3\/3<\/code> Verifying : libsmi-0.4.8-13.el7.x86_64 1\/3<\/code> Verifying : c-ares-1.10.0-3.el7.x86_64 2\/3<\/code> Verifying : wireshark-1.10.14-10.el7.x86_64 3\/3<\/code>Installed:<\/code> wireshark.x86_64 0:1.10.14-10.el7<\/code>Dependency Installed:<\/code> c-ares.x86_64 0:1.10.0-3.el7 libsmi.x86_64 0:0.4.8-13.el7<\/code>Complete!<\/code><\/p>\n

Collect data and show statistics at the end:
\n# tshark -q -z io,stat,30,\"COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission\"<\/code><\/p>\n

Realtime output of source and destination
\n# tshark\u00a0-R tcp.analysis.retransmission<\/code><\/p>\n

Record all data into a binary file:
\n# tshark -i bond0 -w \/temp_data\/test.pcap -F libpcap<\/code><\/p>\n

View detailed output:
\n# tshark -r \/temp_data\/test.pcap -q -z io,stat,1,\\
\n> \"COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission\",\\
\n> \"COUNT(tcp.analysis.duplicate_ack)tcp.analysis.duplicate_ack\",\\
\n> \"COUNT(tcp.analysis.lost_segment) tcp.analysis.lost_segment\",\\
\n> \"COUNT(tcp.analysis.fast_retransmission) tcp.analysis.fast_retransmission\"<\/code><\/p>\n

Sample output:
\n===================================================================
\nIO Statistics
\nInterval: 1.000 secs
\nColumn #0: COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission
\nColumn #1: COUNT(tcp.analysis.duplicate_ack)tcp.analysis.duplicate_ack
\nColumn #2: COUNT(tcp.analysis.lost_segment) tcp.analysis.lost_segment
\nColumn #3: COUNT(tcp.analysis.fast_retransmission) tcp.analysis.fast_retransmission
\n| Column #0 | Column #1 | Column #2 | Column #3
\nTime | COUNT | COUNT | COUNT | COUNT
\n000.000-001.000 0 0 2 0
\n001.000-002.000 0 0 0 0
\n002.000-003.000 0 0 0 0
\n003.000-004.000 0 0 0 0
\n004.000-005.000 0 0 0 0
\n005.000-006.000 0 0 0 0
\n006.000-007.000 0 0 0 0
\n007.000-008.000 0 0 0 0
\n008.000-009.000 0 0 0 0
\n009.000-010.000 0 0 0 0
\n010.000-011.000 0 0 0 0
\n011.000-012.000 0 0 0 0
\n012.000-013.000 0 0 0 0
\n013.000-014.000 0 0 0 0
\n014.000-015.000 5 56 6 5
\n015.000-016.000 7 46 4 4
\n016.000-017.000 9 30 5 3
\n017.000-018.000 6 51 6 6
\n018.000-019.000 4 54 4 4
\n019.000-020.000 1 24 0 1
\n020.000-021.000 0 0 6 0
\n021.000-022.000 0 0 16 0
\n022.000-023.000 4 21 8 4
\n023.000-024.000 14 0 1 0
\n024.000-025.000 25 17 3 1
\n025.000-026.000 0 0 4 0
\n026.000-027.000 21 19 11 2
\n027.000-028.000 34 27 5 3
\n028.000-029.000 3 34 3 3
\n029.000-030.000 3 36 9 3
\n030.000-031.000 0 0 7 0
\n031.000-032.000 23 5 2 1
\n032.000-033.000 0 0 0 0
\n033.000-034.000 3 30 3 3
\n034.000-035.000 1 3 2 1
\n035.000-036.000 14 47 4 4
\n036.000-037.000 2 29 4 2
\n037.000-038.000 1 20 2 1
\n038.000-039.000 0 0 0 0
\n039.000-040.000 0 0 0 0
\n===================================================================<\/code><\/p>\n

By using netstat<\/h3>\n

Get statistics about retransmissions
\n# netstat -s | grep segments<\/code><\/p>\n

Get statistics about packet loss
\n# netstat -s | egrep -i 'loss|retran'<\/code><\/p>\n<\/div>\n

\n

Press CTRL-C to abort and to see the results<\/p>\n<\/div>\n

Results<\/h1>\n

By using tshark<\/h3>\n

<\/p>\n

\"\"<\/p>\n

By using netstat<\/h3>\n

\"\"<\/p>\n

\"\"<\/p>\n","protected":false},"excerpt":{"rendered":"

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