Computer Network (ii)

Three. Network layer (protocol located on host and router,ip/icmp/arp/rarp)

1.2 Types of services available at the network level

Non-connected network services (Datagram service ), connection-oriented services ( virtual circuit Services )

2. Internet Protocol IP

(1) Overview

　　 IP provides unreliable, non-connected datagram delivery services

(2)IP Addressing

The network number of the host and router on the same LAN is the same. Routers have more than 2 IP addresses, one port one, and the network number for each port is different.

The private address can only be used in the intranet, not in the Internet, if the host network to connect with the Internet must be address resolution (NAT).

a:1.x.x.x~126.x.x.x 0 Dedicated Address: 10.0.0.0-10.255.255.255

b:128.1.x.x~191.255.x.x 10 Dedicated Address: 172.16.0.0-172.31.255.255

c:192.0.1.x~223.255.255.x 110 Dedicated Address: 192.168.0.0-192.168.255.255

d:224.x.x.x 1110 Multicast Address

e:240.x.x.x 11110 reserved Address

　Special Address:

The address for which the host number is all 1 is the broadcast address of the network;

The host number is reserved as a network address for all 0;

Loopback Address: 127. x.x.x. Generally used to check if the protocol is installed correctly.

(3) Division of Subnets and construction of networks

　　Subnet and subnet mask

no-class inter-domain Routing (CIDR):128.14.35.7/20. Route aggregation

(4) IP datagram format

3. Inter-network Control Message Protocol ICMP

ICMP messages are encapsulated in an IP datagram and are used to send error and control messages. As with IP datagrams, it is unreliable .

Echo Request and reply message, timestamp request and reply message.

4. Address Resolution Protocol ARP and Inverse Address Resolution Protocol Rarp

The ARP:IP address is mapped to a MAC address.

RARP: for diskless systems?

5. Router Routing Protocol ( third layer network device )

　　Isolated broadcast domain; routing table; static routing and dynamic routing; Internal Gateway Protocol (IGP) and External Gateway Protocol (EGP); Routing protocol (RIP and OSPF)

6.IPV6 (128-bit)

Computer Network (ii)