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Understanding the network.pdf - Back to Home

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will connect in <strong>the</strong> future, it is best <strong>to</strong> use <strong>the</strong> recommended unregistered <strong>network</strong><br />

address spaces:<br />

Class A: 10.0.0.0 255.0.0.0 or /8<br />

Class B: 172.16.0.0 <strong>to</strong> 172.31.0.0 255.255.0.0 or /16<br />

Class C: 192.160.0.0 <strong>to</strong> 192.168.255.0 255.255.255.0 or /24<br />

These spaces are set aside for unregistered <strong>network</strong> use by IANA/ICANN. If you<br />

later decide <strong>to</strong> connect <strong>to</strong> <strong>the</strong> Internet, you can continue <strong>to</strong> use <strong>the</strong> unregistered<br />

space and use a Network Address Translation (NAT) gateway <strong>to</strong> map your<br />

unregistered host's IP datagrams <strong>to</strong> registered IP addresses.<br />

NOTE<br />

Remember, if your IP addressing is not set up correctly, no datagrams will be able<br />

<strong>to</strong> be delivered. When using classful IP addressing, follow <strong>the</strong>se rules:<br />

• Each host interface must have its own unique IP address.<br />

• Each IP subnet must have its own unique IP address space and<br />

corresponding subnet mask.<br />

• On each physical <strong>network</strong> segment, all <strong>the</strong> hosts must use a common unique<br />

IP address space.<br />

• A <strong>network</strong> address of all ones (<strong>network</strong> loopback) and all zeros (<strong>network</strong><br />

broadcast) cannot be used for host addresses (except under certain<br />

conditions when classless addressing is used).<br />

IP Datagram Delivery Process<br />

Two processes, routing and forwarding, accomplish IP datagram delivery. The<br />

routing process is how <strong>the</strong> path <strong>to</strong> <strong>the</strong> destination host is discovered and route<br />

selection accomplished. Routing is a Layer 3 activity concerned with <strong>the</strong> delivery (in<br />

most cases) of datagrams between two unique physical identities. Forwarding is <strong>the</strong><br />

activity of placing <strong>the</strong> IP datagram in<strong>to</strong> physical transport (Layer 2) frames (such as<br />

E<strong>the</strong>rnet, FDDI, Frame Relay) <strong>to</strong> carry <strong>the</strong> IP datagram across <strong>the</strong> physical <strong>network</strong><br />

segment <strong>to</strong> <strong>the</strong> destination host or intermediate router.<br />

The IP datagram delivery process is based on a concept known as hop-<strong>to</strong>-hop<br />

forwarding. Because IP is a connectionless pro<strong>to</strong>col, IP datagrams are forwarded on<br />

next-hop basis. The essence of this idea is that <strong>the</strong> forwarding host may not know<br />

exactly how <strong>to</strong> reach <strong>the</strong> destination, but it does know a host that claims <strong>to</strong> know <strong>the</strong>

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