Network Layer

See Figure  on page  .

  [IMAGE ]
Figure: A IP Network

The network layer communication is from IP to IP using data grams connected together with routers with the aid of Domain Name Service (DNS).

See Figure  on page  .

  [IMAGE ]
Figure: A IP Routing Table

The network consists of many networks connected together by routers. At each computer on the network is a simple routing table that sends packets to the router. At each router is a much larger table representing routing information for the entire network. Given a destination IP, the table returns the next hop.

See Figure  on page  .

  [IMAGE ]
Figure: A DNS Table

The DNS materializes a name space for all the computers in a domain. DNS will map computer names to IPs.

See Figure  on page  .

  [IMAGE ]
Figure: A IP Packet

To prevent cycles, each packet has a maximum hop count. Each time the packet passes through a router, the hop count is decremented. If the count reaches zero, the packet is dropped.

If the packet is too big for the physical layer, the packet is fragmented into smaller pieces. Each piece is then delivered and the packet is reconstructed at the destination.