Things you should know about IP address
RFC 5735 -- Special Use IPv4 Addresses
0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
network. Address 0.0.0.0/32 may be used as a source address for this
host on this network; other addresses within 0.0.0.0/8 may be used to
refer to specified hosts on this network
What is an IP address? at
Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts.
Computers normally show an address of 0.0.0.0 when they are not connected to a TCP/IP network. Having this address, a computer cannot be reached or communicate with any other devices over IP.
And, this can be confusing sometimes -- but, all it means is
when you see packets with source IP
0.0.0.0, just assume it means 'Null',
and, if you see it being used to match IP addresses, take it as a 'wildcard'.
TCP/IP software applications also use 0.0.0.0 as a programming technique to monitor network traffic from any valid IP address. While connected computers do not use this address, messages carried over IP sometimes include 0.0.0.0 inside the header when the source of the message is unknown.