Network interconnection devices
Segments on a network can be interconnected using a:
Figure 4-7 OSI Representations of Network Devices
A repeater is a physical layer (OSI model) device that amplifies the signal of one segment onto one or more other segments. Repeaters are used to extend the maximum possible distance between end nodes on a segment. They are completely transparent to the sending and receiving nodes.
A bridge is a data link layer device used to interconnect cable segments locally or over wide area network links. Instead of simply amplifying a signal as repeaters do, bridges retransmit packets received on one segment onto another segment. Bridges are considered data link layer devices because they examine the data link (or MAC header) portion of packets before retransmitting them onto other segments. There are two predominant types of bridge: source routing bridges and transparent bridges.
Figure 4-8 Sample Transparent Bridge
After examining the packets transmitted on both segments, the bridge creates a table that tracks which nodes exist on each segment. With this table, the bridge can filter unnecessary traffic. For instance, if node 1 sends a packet to node 5, the bridge will not retransmit that packet on its port B. It will, however, retransmit packets sent from node 1 to node 7. Like repeaters, transparent bridges -- as their name implies -- are transparent to the sending and receiving nodes.
Routers interconnect different network segments. However, unlike bridges, routers, by definition, are network layer devices (see Figure 4-7). In other words, routers receive their instructions for forwarding a packet from one segment to another from a network layer protocol.
NetWare-compatible routers are available with NetWare or from third-party manufacturers. The routers that come packaged with NetWare have actually been misnamed ``bridges'' in the past. The NetWare routers include what has been called the internal bridge within NetWare file servers and the external bridge installed at workstations. Novell has officially renamed these two devices ``internal router'' and ``external router''.
NetWare-compatible routers can be configured to interconnect two or more segments. Each of these segments, however, must be assigned a unique network number to distinguish it from other segments on the network. A segment's network number must be configured into each of the routers connected to that segment. The network number serves as a common address for each node connected to a segment. For more information on assigning a segment's network number, see Appendix A, ``Configuration parameters'' in Configuring Network Connections.