tailieunhanh - Practical TCP/IP and Ethernet Networking- P39

Practical TCP/IP and Ethernet Networking- P39: 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 | 172 Practical TCP IP and Ethernet Networking ROUTE The route command is used to configure network routing tables. This may be a tedious task but is sometimes necessary for reasons of security or because a specific route has to be added. The following shows the route options. C route Manipulates network routing tables. ROUTE -f command destination MASK netmask gateway METRIC metric -f Clears the routing tables of all gateway entries. If this is used in conjunction with one of the commands the tables are cleared prior to running the command. command Must be one of four PRINT Prints a route ADD Adds a route DELETE Deletes a route CHANGE Modifies an existing route destination Specifies the destination host. MASK Specifies that the next parameter is the netmask value. netmask Specifies a subnet mask value to be associated with this route entry. If not specified it defaults to . METRIC Specifies that the next parameter metric is the cost for this destination All symbolic names used for destination are looked up in the network database file NETWORKS. The symbolic names for gateway are looked up in the host name database file HOSTS. If the command is PRINT or DELETE wildcards may be used for the destination and gateway or the gateway argument may be omitted. Diagnostic notes Invalid MASK generates an error that is when DEST MASK DEST. Example route ADD MASK The route addition failed 87 Examples route PRINT route ADD MASK METRIC 3 destination Amask Agateway Ametric route PRINT route DELETE route PRINT C The route table exists on both hosts and routers. An individual entry is read from left to right as follows If a message is destined for network with subnet mask then route it through to the gateway address . Remember that a HostID equal to 0 as used here does not refer to a specific host but rather to the .