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Routing

Routing is the process of moving network data (packets) from one network to another across a device that is connected to multiple networks. The routing function is performed by a devices called a 'router'.

NOTE: It is absolutely critical that you understand how Internet Protocol (IP) works before you try to understand IP routing. If you don't understand the basics of Internet Protocol, you should go back and learn it now.

THE LAWS OF IP

1. The Default Gateway is for reaching OFF NETWORK hosts (hosts not on the local subnet).
2. Default gateways are used for contacting hosts external to the local network or subnet.
3. In general, you route TO DESTINATIONS, not  from sources.
4. Internet Protocol should not forward broadcasts off the local subnet. This is a congestion control mechanism built into all routers that comply with standards for IP routing.
5. Routing is not used for hardware broadcasts which by definition are local traffic (ARP, DHCP, NetBIOS, NetBEUI etc.) see RFC 919.
6. The broadcast address 255.255.255.255 SHOULD NOT BE FORWARDED (per RFC 919, section 7.0). If such forwarding were broadly permitted, the Internet would be flooded with broadcast traffic.