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Question ? How can I do some network troubleshooting ?   [
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  • TCPDump

    tcpdump -i [Network-Device] host [IP-Address]

    In case you want to filter more specifically, b.e. filter on host and protocol, use this

    tcpdump -i [Network-Device] -x 'ip host [hostname] and port http'

  • Ethereal
    Note that newer versions are called wireshark for the GUI Based tool, the CLI based tool is called tshark - replace were appropriate

    tethereal -i [Network-Device]

    If you want to limit on a specific IP-Address, b.e. your workstation IP, use the following

    tethereal -i [Network-Device]  -R ip.addr==[IP-Address]

    and if you have the webserver running on a different port as 80 - tell ethereal what tcp-port to interprete as http traffic with the following

    tethereal -i [Network-Device]  -d tcp.port==[Port-Nr],http -R ip.addr==[IP-Address]

    Another easy way to filter is:

    tethereal -i [Network-Device] host [host-IP] and port [Port-Nr.]

    If you want to dump the output to a file - append: -w output.dump to these strings - and you'll have all data dumped to these files - you can later read/open with ethereal for analisys.

  • IPtraf - provides you an easy way to identify non clean traffic. This means, even if tethereal and tcpdump show you some data, iptraf will not show you a packet count increase in case the data is valid, e.g. a wrong setup VLAN (Unidirectional traffic, missing parts of the tcp/ip traffic messages etc.

  • In case you have https-traffic to monitor - you can use ssldump to have a look at the traffic. this troubleshooting method is also very keen in case you see loads of ssl-decode errors. Try out the following:

    ssldump -ni eth1 -d -k [pem-key] host [host-ip]

  • A very keen solution is to also tunnel the traffic from your workstation into an internal machine - to have a specific IP-Address to filter through the advanced recorder. This can be reached by using ssh in tunnel mode from your local machine (note that you'll need a local cli-based ssh solution on the workstation you are working from:

    ssh -L [client-IP]:[client-Port]:[remote-IP]:[remote-port]

    once done - connect to the application by using http://localhost[client-port]


Entered by smurphy on Tuesday, 21 October 2008 @ 09:43:36  
Linux General - Common Linux problems, # Hits: 86541
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