frames. These bridges are called learning bridges due to this advanced functionality. Most of the functionality of bridges is now included in switches.
Routers Routers are used to connect two or more networksegments. Routers use IP addresses to determine the source and destination of the data packet. Typically, routers receive the data packet, determine the destination IP address, and forward the packet to the next hop (which may either be the final destination of the packet or another router on the path). Routers can be implemented as a software service or as a dedicated hardware device. A wired or wireless router in a home network is an example of a small networkrouter that connects the home networkto the ISP’s network. Routers communicate to each other using routing protocols. Routers maintain a list of IP addresses in routing tables. Routing tables can be built statically or dynamically as discussed in the following sections: Static routing When static routing is used, administrators manually configure routing tables by entering appropriate routing information. This method works only for very small networks. Dynamic routing In a dynamic routing environment, routers use Routing Information Protocol (RIP) or Open Shortest Path First (OSPF) to build, maintain, and advertise their routing tables. Most networks are based on dynamic routing.
Networking protocols Networking protocols allow computers to communicate to each other through the networking media. Some of these protocols are common to all operating systems while others are platform-dependent. This section covers a brief description of the commonly used protocols TCP/IP, IPX/SPX, and NetBEUI. Transmission Control Protocol/Internet Protocol (TCP/IP). TCP/IP is a set of several protocols. It is the most widely used protocol suite in private networks as well as on the Internet. TCP/IP is not proprietary to any organization but is a public protocol suite. It is a fully routable protocol and is supported by all major networkand desktop operating systems. Some of the well-known TCP/IP protocols and their functions are listed in Table 2-12. Table 2-12. TCP/IP protocols and their functions Protocol Internet Protocol (IP) Transmission Control Protocol (TCP) User Datagram Protocol (UDP)
Function IP is a connection-less protocol that provides IP addressing and routing functions. TCP is a connection-oriented protocol that guarantees delivery, flow control, error detection, error correction, and packet sequencing. UDP is a connection-less transport protocol. It does not provide guaranteed delivery of data.