Cabletron Systems CyberSWITCH CSX101 User's Information Manual

About the CyberSWITCH 100 RouterCyberSWITCH 100 Advanced User Information 13Bridging and RoutingBridging — Bridging connects two or more LANs together so that all devices share the samelogical LAN segment and network number. The bridge examines a portion of each network framecalled the header. This header contains control information for the frame. The bridge compares thedestination address of the frame with the address from which the frame was received. If theaddress indicates that the sending station and the destination station are on the same side of thebridge, the frame is discarded. If the addresses indicate that the sending station and the receivingstation are not on the same side, then the bridge forwards the frame to its other interface.During this process, the bridge formulates a table that allows it to identify which stations areconnected to which LAN segment. The destination addresses of received frames are compared tothis address table and decisions are made to discard, or forward frames, based on the outcome.Transparent bridging allows locally connected devices to send frames to all devices as if they arelocally connected.Bridging allows frames to be sent to all destinations regardless of the network protocols used. Itallows protocols that cannot be routed (such as NETBIOS) to be forwarded and optimizesinternetwork capacity by localizing traffic on LAN segments. A bridge extends the physical reachof networks beyond the limits of each LAN segment. Filters are used to increase network securityin bridged networks.Routing — Routing provides a way to transfer data from source to destination over differentLAN and WAN links using one or more network protocol formats. Routing relies on routingaddress tables to determine the best path for each packet. Routing tables can be seeded; i.e.,addresses for remote destinations are placed in the table along with network address masks and ametric for path latency. Routing tables are also built dynamically; i.e., the location of remotestations, hosts, and networks, are updated from broadcast packet information. Routing helps toincrease network capacity by localizing traffic on LAN segments and reducing the number ofbroadcasts that would result from bridged traffic. Routing also provides security by isolating trafficon segmented LANs. Routing extends the reach of networks beyond the limits of each LANsegment.CyberSWITCH 100 Bridging and Routing — The CyberSWITCH 100 can operate as a bridge,as a router, or as both (sometimes called a brouter). The CyberSWITCH 100 operates as a routerfor network protocols that are supported when routing is enabled. The router operates as a bridgewhen bridging is enabled. When both bridging and routing are enabled, routing takes precedenceover bridging; i.e., the router uses the protocol address information of the packet to route thepacket to the correct destination and if the protocol is not supported, the router uses the MACaddress information to bridge the packet.