Chapter 15Configuring BridgingIntroductionThe FRM supports transparent "Spanning Tree" bridging of non-routable LAN traffic(e.g., NetBIOS, DECnet, AppleTalk) over frame relay between 802.3/Ethernet or802.5/Token Ring LANs. The FRM also supports translational bridging betweenEthernet and Token Ring LANs. (For more information on bridging, refer to IEEEstandard 802.1d.)Bridging support includes:l Encapsulation of Ethernet and Token Ring traffic per RFC 1490 for trans-mission over frame relayl Transparent Spanning Tree (802.1) bridgingl Translational bridging between Ethernet and Token Ring LANsl Compatibility with Source Route Bridge environmentsl "Self-learning" of MAC addresses for core bridgingl Forwarding of non-routable LLC traffic such as NetBIOS, DECnet, AppleTalk,LAT, and VINESl Routing/bridging of IP and IPX trafficl MAC address filteringl NetBIOS name filteringl Bandwidth allocationl Multivendor interoperability with other IEEE 802.1d devicesRouting transmits each packet based on its level-3 address, while bridging transmitseach frame based on its level-2 address. Athough some traffic can be either routed orbridged, there is usually an advantage to doing one over the other. For instance,bridging is generally easier to configure; however, routing can be more versatile.IP and IPX traffic can also be bridged. (Bridging can be enabled individually for IP orIPX; if enabled for either, all traffic of that type will be bridged.)Neither IP (because of its ARP frames) nor IPX (because of its MACaddressing structure) can be bridged successfully between Ethernet andToken Ring LANs. (However, they can be routed between different LANtypes.)
