ICMP flood protection in Tomato?

Discussion in 'Tomato Firmware' started by cpgbg, Apr 12, 2008.

  1. cpgbg

    cpgbg LI Guru Member


    I have noticed strange behaviour when tracing multiple targets, so I made an experiment. I opened 2 command prompt windows and issued this command in both:

    ping -t -i 1 www.linksysinfo.org

    Note: -i 1 sets TTL to 1

    If I run this in just one window it is OK

    But when I start 2 of them I start to receive timeouts in both windows.

    It seems that while one is getting response, the other gets timeout and vise versa.
    Does anyone know what is causing this?
  2. RonWessels

    RonWessels Network Guru Member

    Ping is an ICMP protocol packet. ICMP is layered directly on IP. This means that that identification of the packet source is done on a machine basis. Protocols like UDP and TCP have the concept of a "port" which is used to identify the particular process on the machine performing the communication. ICMP doesn't, so there's no differentiation between the packets coming from and returning to your two "ping" windows. Hence the OS picks one at random for every reply that is received.

    For more information, I'd recommend the Wikipedia articles on IP, ICMP and UDP.
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