Sunday, August 15, 2010
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A network is a physical group of computers wired together so that they can communicate directly with each other using the same data link protocol and without being connected by routers. For instance, any computer on an office Ethernet network can address any other computer on the network directly—there's no need to forward information between two different shared media networks (for instance, between an Ethernet and a token-ring network).
Computers may be connected with hubs, switches, or bridges but remain a single network because data can be transmitted between any two computers over the same data link protocol. In some cases, switches perform minor changes in the data link protocol (for instance, bridging fast Ethernet and Ethernet) because these technologies use the same data link protocols but operate at different speeds.
The terms transport protocol and network protocol are somewhat synonymous.
Transport protocol is the more generic of the two and includes protocols such as NetBEUI that cannot be used to forward data between networks. Network protocol Is specific to protocols such as TCP/IP or IPXJSPX that can forward data between networks. Specifically, network protocols provide packet forwarding between networks (the IP portion of TCP/IP), and transport protocols provide flow control, error correction, and connection services (the TCP portion of TCP/IP), Most actual software services perform both with the same software. Microsoft uses the term transport protocol to refer to any suite that provides all these services.
An internetwork is a group of networks connected by routers that are configured to forward (or route) data between the networks based on a set of forwarding rules. The different networks do not need to be of the same data link type, because the router (sometimes called a gateway in UNIX circles) can Connect to any type of data link. The router examines every packet's destination address and determines which of its ports is closest to the destination computer. One of the following events happens:
• The router can match the packet directly to an entry in the routing table and transmit the packet directly to the host or router.
• If the router doesn't have enough information to determine where a packet should go, it simply sends the packet to another router (its default gateway) that it trusts will know how to deal with the packet.
• If a router does not know how to forward the packet and does not have a default gateway, the destination is unreachable because the two networks are not connected properly.
Any computer with routing software can function as a router, but networks that use non dedicated routers experience more time delays (latency) and hardware bottlenecks than networks that use dedicated routers do.
Dedicated routers are simply computers that are optimized for the routing function and do not perform other general-purpose functions. They do not require video displays or keyboards, usually do not have hard disk drives, and may use esoteric RISC microprocessors; otherwise, dedicated routers are similar to general-purpose computers in hardware, and most run a small variant of the UNIX operating system. They are rather expensive—generally twice the price of a multihomed server capable of performing the same routing function. You may find you can live with the lower overall throughput of a multihomed server acting as a router in your networks.
The Internet is a single large internetwork based on the TCP/IP protocol suite. Nearly every large corporation and university in the world, as well as many small businesses and individuals, are connected to the Internet. Intranets are private networks that may or may not be attached to the Internet; intranets are also based on the Internet protocols. TCP/IP is a suite of protocols that the government and universities have developed over the last two decades that enable very large networks to be connected. The rest of this chapter discusses the various protocols embodied by the TCP/IP suite that are most important to the creation and connection of networks.
The TCP/IP suite embodies many other protocols, but they either are not nearly as important or are not implemented in many versions of the suite. The entire suite is referred to collectively as TCP/IP (because Transmission Control Protocol and Internet Protocol are the two most common and most important protocols), or as the Internet protocols.
Networks and Routing
A network is a physical group of computers wired together so that they can communicate directly with each other using the same data link protocol and without being connected by routers. For instance, any computer on an office Ethernet network can address any other computer on the network directly—there's no need to forward information between two different shared media networks (for instance, between an Ethernet and a token-ring network).
Computers may be connected with hubs, switches, or bridges but remain a single network because data can be transmitted between any two computers over the same data link protocol. In some cases, switches perform minor changes in the data link protocol (for instance, bridging fast Ethernet and Ethernet) because these technologies use the same data link protocols but operate at different speeds.
The terms transport protocol and network protocol are somewhat synonymous.
Transport protocol is the more generic of the two and includes protocols such as NetBEUI that cannot be used to forward data between networks. Network protocol Is specific to protocols such as TCP/IP or IPXJSPX that can forward data between networks. Specifically, network protocols provide packet forwarding between networks (the IP portion of TCP/IP), and transport protocols provide flow control, error correction, and connection services (the TCP portion of TCP/IP), Most actual software services perform both with the same software. Microsoft uses the term transport protocol to refer to any suite that provides all these services.
An internetwork is a group of networks connected by routers that are configured to forward (or route) data between the networks based on a set of forwarding rules. The different networks do not need to be of the same data link type, because the router (sometimes called a gateway in UNIX circles) can Connect to any type of data link. The router examines every packet's destination address and determines which of its ports is closest to the destination computer. One of the following events happens:
• The router can match the packet directly to an entry in the routing table and transmit the packet directly to the host or router.
• If the router doesn't have enough information to determine where a packet should go, it simply sends the packet to another router (its default gateway) that it trusts will know how to deal with the packet.
• If a router does not know how to forward the packet and does not have a default gateway, the destination is unreachable because the two networks are not connected properly.
Any computer with routing software can function as a router, but networks that use non dedicated routers experience more time delays (latency) and hardware bottlenecks than networks that use dedicated routers do.
Dedicated routers are simply computers that are optimized for the routing function and do not perform other general-purpose functions. They do not require video displays or keyboards, usually do not have hard disk drives, and may use esoteric RISC microprocessors; otherwise, dedicated routers are similar to general-purpose computers in hardware, and most run a small variant of the UNIX operating system. They are rather expensive—generally twice the price of a multihomed server capable of performing the same routing function. You may find you can live with the lower overall throughput of a multihomed server acting as a router in your networks.
The Internet is a single large internetwork based on the TCP/IP protocol suite. Nearly every large corporation and university in the world, as well as many small businesses and individuals, are connected to the Internet. Intranets are private networks that may or may not be attached to the Internet; intranets are also based on the Internet protocols. TCP/IP is a suite of protocols that the government and universities have developed over the last two decades that enable very large networks to be connected. The rest of this chapter discusses the various protocols embodied by the TCP/IP suite that are most important to the creation and connection of networks.
The TCP/IP suite embodies many other protocols, but they either are not nearly as important or are not implemented in many versions of the suite. The entire suite is referred to collectively as TCP/IP (because Transmission Control Protocol and Internet Protocol are the two most common and most important protocols), or as the Internet protocols.
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