If You See This:

It Means This:

Entire IP address is all zeros

As a source address: "This host"

As a destination address: "I don't know the correct IP address to use so I'll use all zeros" This was also the early form of the IP destination address which meant "BROADCAST" but this usage is now considered obsolete.

Entire IP address is all ones.

This is called a LIMITED BROADCAST. This is a broadcast to all hosts on the current subnet. A router will NOT forward this type of broadcast to other networks.

NETWORK = A valid network number.
SUBNET = A valid subnet number.
HOST = All ones.

This is called a DIRECTED BROADCAST. This is a broadcast to all hosts on the specified network and subnetwork. A router WILL forward this frame for broadcast on the specified destination network and subnetwork.

127.x.x.x

This is a local loopback address. Frames sent to this address will be looped back and returned to the sending application without actually being sent onto the network.

0.x.x.x, 128.0.x.x, 191.255.x.x, 129.0.0.x, 223.255.255.x

These address constructions are reserved by the Network Information Center.