21 BRIDGING CONFIGURATIONWhen configuring bridging functionalities, go to the following sections for theinformation you are interested in:■ “Bridging Overview” on page 405■ “Bridging Configuration Task List” on page 409■ “Displaying and Maintaining Bridging Configurations” on page 412■ “Transparent Bridging Configuration Examples” on page 412n Presently the devices support only transparent bridging, so this document providesinformation about transparent bridging only.Bridging OverviewIntroduction to Bridging A bridge is a store-and-forward device that connects and transfers traffic betweenlocal area network (LAN) segments at the data-link layer. In some small-sizednetworks, especially those with dispersed distribution of users, the use of bridgescan reduce the network maintenance costs, without requiring the end users toperform special configurations on the devices.In applications, there are four major kinds of bridging technologies: transparentbridging, source-route bridging (SRB), translational bridging, and source-routetranslational bridging (SR/TLB).Transparent bridging is used to bridge LAN segments of the same physical mediatype, primarily in Ethernet environments. Typically, a transparent bridging devicekeeps a bridge table, which contains mappings between destination MACaddresses and outbound interfaces.Presently the devices support the following transparent bridging features:■ Bridging over Ethernet■ Bridging over point-to-point (PPP) and high-level data link control (HDLC) links■ Bridging over X.25 links■ Bridging over frame relay (FR) links■ Inter-VLAN transparent bridging■ Routing and bridging are simultaneously supportedMajor Functionalities ofBridgesMaintaining the bridge tableA bridge relies on its bridge table to forward data. A bridge table consists twoparts: MAC address list and interface list. Once connected to a physical LAN
