tailieunhanh - Practical TCP/IP and Ethernet Networking- P37

Practical TCP/IP and Ethernet Networking- P37: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter | 9 TCP IP utilities Objectives When you have completed study of this chapter you should able to apply the following utilities Ping ARP NETSTAT NBTSTAT IPCONFIG WINIPCFG tracert ROUTE Introduction The TCP IP utilities are discussed throughout the book. This section is designed to bring them all together in one section for ease of reference as they are very important in network management and troubleshooting. Most of the older utilities are DOS-based. However more and more Windows-based utilities are becoming available many of them as freeware or shareware. Ping packet Internet groper Pinging is one of the easiest ways to test connectivity across the network and confirm that an IP address is reachable. The DOS ping utility uses ICMP to forward an echo request packet to the destination address. The destination then responds with an ICMP echo response packet. Although the test seems trivial at first sight it is a powerful diagnostic tool and can demonstrate correct operation between the Internet layers of two TCP IPutilities 163 hosts across a WAN regardless of the distance and number of intermediate routers involved. Technically speaking the ping utility can only ping an IP address. This is due to the fact that the ICMP messages are carried within IP datagrams which require the source and destination IP addresses in the header. Without this feature it would have been impossible to ping across a router. If therefore the user does not know the IP address the name resolver on the local host system has to look it up . via the domain name system or in the hosts file. The IP datagram in turn is transported by means of a network interface layer frame . Ethernet which requires in its header the MAC addresses of the source and destination nodes on the local network. If this is not to be found in the ARP cache the ARP protocol is invoked in order to obtain the MAC address. The result of this action the mapping of MAC address against IP address is then .