Junos OS

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  • 1.  help me to understand this traffic pattern

    Posted 08-22-2011 22:42

    when i run monitor traffic command it show me this output

    13:28:02.565008  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:02.565023  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:02.565425  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:02.565439  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:03.581009  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:03.581025  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:03.581309  In arp who-has 192.168.0.1 tell 192.168.1.15
    13:28:03.581323  In arp who-has 192.168.0.1 tell 192.168.1.15

    Out IP truncated-ip - 272 bytes missing! 192.168.1.1.bootps > 255.255.255.255.bootpc: BOOTP/DHCP, Reply, length 300
    13:28:10.963482 Out IP truncated-ip - 272 bytes missing! 192.168.1.1.bootps > 255.255.255.255.bootpc:

    BOOTP/DHCP, Reply, length 300

    13:28:23.913378  In arp who-has 192.168.10.1 tell 192.168.1.109
    13:28:23.913394  In arp who-has 192.168.10.1 tell 192.168.1.109
    13:28:23.913561  In arp who-has 192.168.10.1 tell 192.168.1.109
    13:28:23.913590  In arp who-has 192.168.10.1 tell 192.168.1.109
    13:28:23.913870  In arp who-has 192.168.10.1 tell 192.168.1.109
    13:28:23.913884  In arp who-has 192.168.10.1 tell 192.168.1.109

     

     

    kindly help me to understand the two things

    i am not using 192.168.10.1 and 192.168.0.1 in my network then why it is showing in monitor traffic

    why it is showing 272 byte missing

     

    thanku

     

     



  • 2.  RE: help me to understand this traffic pattern
    Best Answer

    Posted 08-23-2011 01:38

    >  help me to understand this traffic pattern

     

    Hi Rohit,

     

    Let me try - it is relatively straightforward..

     

    These lines:

     

    > 13:28:02.565008  In arp who-has 192.168.0.1 tell 192.168.1.15
    > 13:28:02.565023  In arp who-has 192.168.0.1 tell 192.168.1.15

     

    mean that the host at 192.168.1.15 is trying to reach host 192.168.0.1, which is down/not answering.

    The same happens here:

     

    > 13:28:23.913378  In arp who-has 192.168.10.1 tell 192.168.1.109
    > 13:28:23.913394  In arp who-has 192.168.10.1 tell 192.168.1.109

     

    where 192.168.1.109 is trying to reach 192.168.10.1, which is down. 

    You would get the exact same behaviour if you run a packet capture program on your PC (i.e. Wireshark) and try to ping an unassigned address on your LAN.

    So, if you are not using those two addresses, this traffic pattern is not surprising at all. If you are really curious, you may want to check why 192.168.1.15 and 192.168.1.109 are trying to reach those non-existent addresses.

     

    About this, instead:

     

    > 13:28:10.963482 Out IP truncated-ip - 272 bytes missing! 192.168.1.1.bootps > 255.255.255.255.bootpc:

    > BOOTP/DHCP, Reply, length 300

     

    .. it is not a real problem, and the datagram is not really truncated; it is only that by default "monitor traffic" only captures up to the transport header of every frame.

    If you want to capture the whole frame, add "size 1500" (Ethernet MTU) to your "monitor traffic" command, and the frames will no longer show as truncated. One word of warning:  I am told that the 'size' knob does not work on some low-end j-series though; can you try it on your?

     

    Thanks,

     Saverio