icmp(7)                             CLIX                             icmp(7)



  NAME

    icmp - Internet Control Message Protocol device

  DESCRIPTION

    The icmp device, the Internet Control Message Protocol (ICMP), provides
    feedback about problems in the communications environment pertaining to
    processing Internet Protocol (IP) datagrams.  It also supplies some basic
    utilities such as echo functionality and Internet subnet mask maintenance.
    While ICMP uses IP for support as if it were a higher-level protocol, it
    is actually an integral part of IP and the ip STREAMS driver.

    ICMP error messages pertaining to datagrams sent by udp can be retrieved
    with the t_rcvuderr() call.

    The following ICMP messages are supported:

    Echo   Sends a message to a specified host with the intent of the
           destination host returning the same message to the original source.

    Echo Reply
           Sends a message in response to an echo request.  This message
           should be identical to the original echo request.

    Address Mask Request
           Broadcasts a message requesting the subnet mask for an interface.

    Address Mask Reply
           Sends a message with the correct subnet mask in response to an
           Address Mask Request (if the interface is designated an
           authoritative agent).

    Timestamp
           Sends a message to a specific host requesting a Timestamp Reply.
           The format of the Timestamp in this implementation is Hz since the
           last time the system was booted (standard Timestamp is milliseconds
           since midnight UT).

    Timestamp Reply
           Sends a message with a completed timestamp in response to a
           Timestamp message.

    Destination Unreachable
           Sends an error message to a host to indicate that the destination
           to which it is trying to send is unavailable.  The different types
           of Destination Unreachable messages include the following:

           ⊕  net unreachable

           ⊕  host unreachable



  2/94 - Intergraph Corporation                                              1

  icmp(7)                             CLIX                             icmp(7)



           ⊕  protocol unreachable

           ⊕  port unreachable

           ⊕  fragmentation is needed and the ``don't fragment'' bit in the IP
              header is set source route failed

    Redirect
           Sends an error message to inform a host of a better route through
           which a given destination may be reached.

    Source Quench
           Sends an error message request that a source will slow down its
           transmission rate because the destination is being overwhelmed.

    Time Exceeded
           Sends an error message to a source to indicate one of the following
           two conditions:  time to live for a datagram has been exceeded in
           transit, or fragment reassembly time for a datagram has been
           exceeded.

    Parameter Problem
           Sends an error message to a source to indicate that an erroneous
           value has been detected in a protocol header field.  The offset
           field in the Parameter Problem message is set to indicate the
           header field in which the error was detected.

  FILES

    <sys/dod/icmp.h>   ICMP definitions and message formats.

  RELATED INFORMATION

    Files:  inet(7), ip(7)




















  2                                              Intergraph Corporation - 2/94