Groups of machines with similar addresses are considered to be part of the same logical subnet.

One method of assigning IP addresses is DHCP in which addresses typically are issued by a DHCP server running on one or more hosts.

If one of these machines is on the same subnet as its clients, the DHCP server can respond to their broadcast DHCP requests and issue an address.

But the DHCP servers may be hosted on a different subnet and, by default, most routers do not pass broadcast messages to nodes outside their own subnet.

If a DHCP client outside the DHCP servers subnet broadcasts an address request, it is the helper that forwards the message to the DHCP server.

The server then chooses an address and sends the client a unicast message, using the helper to send the message back to the clients subnet.

The address is reserved for a limited time while the DHCP server waits for a response.

If the client responds with another broadcast message, the DHCP server distributes the address.

To disable the forwarding of broadcast packets to specific addresses, use the no form of this command.

Since these ports are used by NetBIOS to help determine network configuration the added broadcasts can confuse the system.

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Ip Helper Address