The last chapter, talking about the transport layer, this chapter talking about the next layer, the network layer.
The transport layer is dependent on the host network layer communications services to host, to provide various forms of communication process to process.
Network layer into two portions, the data plane and control plane. This chapter is mainly about the former, the data plane.
Role of network layer: launching the packet to a mobile host from a host station receives. It requires two important functions: forwarding and routing .
Forwarding: refers to the transfer of a packet from one input link to the appropriate interface to router local link interface output operation. Forwarding time for a short time (typically a few nanoseconds) with hardware.
Routing: determining network-wide packet processing-end path from source to destination is taken. Much longer (a few seconds), implemented in software.
The key elements of each network router: forwarding .
Network Service Model
It defines a packet transport characteristics between the transmitting end and the receiving end of the system.
The network layer provides a single service, called best-effort service. That involves a variety of services, not guaranteed.
Router works
Forwarding the network layer: i.e., to actually link a packet from the router to the appropriate egress link.
Internet Protocol: IPV4, addressing, IPV6 and others.
IP addressing is to have mastered the Internet network layer.
IPV4 datagram format
The network layer packets are called datagrams.
The meaning of each part of this reference.
Datagram fragmentation
The data in the IP datagram is fragmented into two or more smaller IP datagram encapsulation the IP datagrams smaller by a separate link layer frame - referred to as sheet (fragment).
When the host receives an object from a series of the same original datagram, it is necessary to determine whether some of the some of the original large data slice packets of the datagram. So there will be a process of reassembly.
IPv4 addressing
Host and link boundary is called before the physical interface. Each host and router interfaces have their own IP address.
Each IP address length is 32 bits (4 bytes), a total of 32 power 2 ip address. Dotted decimal notation: 193.32.216.9.
Dynamic Host Configuration Protocol (DHCP): allows a host to automatically obtain an ip address.
ipv6: ipv4 protocol address space is exhausted, a new ip protocol development.