Reference Manual


icmap - interact with the ICMP mapping mechanism
icmap [ifn|clear [on|off]]
Command icmap is used to turn ICMP mapping on or off for a specified interface. The command can also be used to clear the entire ICMP mapping table. If no arguments are specified, the command prints the setting of each interface's ICMP mapping flag as well as the contents of the ICMP mapping table.
The ICMP mapping table contains the IP source address of an outgoing ICMP Echo Request packet as well as the first 8 bytes of that packet. When an ICMP Echo Reply arrives from the Internet, NAT32 determines the address of the private machine to receive that packet by matching the 16-bit one's complement sum of the first 8 bytes of the packet with that of an entry in the table. The entry is cleared if a match is found.

NAT32 will not unmap any other incoming ICMP packet types except ICMP Time Exceeded packets received in response to an outgoing Echo Request. This allows utilities such as Traceroute to work correctly, even if several private machines at a time are running such a program.

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