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IP Routing

There are two levels of complexity involved in IP routing:
 
Local delivery
 
When the IP software is presented with a datagram for delivery, it first checks the network/subnet part of the destination address to see if matches its own network/subnet number -- the current netmask is used to discover if these match. If the network/subnet part does match, then the datagram can be delivered locally, and is simply handed to the physical network delivery system (typically an Ethernet device driver) for direct delivery over the local network.
 
Internet delivery
 
If the network numbers are different, then the datagram must be sent to a directly-connected router (or IP gateway), using direct delivery as above, for "on-delivery" across the Internet. Note that when the datagram is received at the router, its destination IP address is not that of the router.
 

 
Lecture 12: IP Networks Copyright © 2002 P.Scott, La Trobe University Bendigo.



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