0.0.0.0 is in the 0.0.0.0/8 block also know as "this" network.
The 0.0.0.0 IP address or 0.0.0.0/32 block may be used as a source address for this host on this network.
This host on this network MUST NOT be sent, except as
a source address as part of an initialization procedure
by which the host learns its own IP address.
[ RFC1122, Section 22.214.171.124 ]
[ RFC1122 Section 126.96.36.199 ]