1-2 C HAPTER 1: G ETTING S TARTEDPort Connections10BASE-T PortsThe Switch has 12 or 24 10BASE-T ports config-ured as MDIX (cross-over), which provide a full10Mbps bandwidth to attached endstations. Maxi-mum segment length is 100m (328ft) over grade 3,4, or 5 twisted pair cable.As these ports are configured as MDIX (cross-over),you need to use a cross-over cable to connect todevices whose ports are MDIX-only. Most of the10BASE-T ports in 3Com devices are MDIX-only.100BASE-TX PortThe Switch has a single Fast Ethernet 100BASE-TXport configured as MDIX (cross-over), which providesa 100Mbps connection to, for example, a localserver. The maximum segment length is 100m(328ft) over grade 5 twisted pair cable.As this port is configured as MDIX (cross-over), youneed to use a cross-over cable to connect to deviceswhose ports are MDIX-only. Most of the100BASE-TX ports in 3Com devices are MDIX-only.Plug-in ModuleA slot at the rear of the unit can take a Plug-inModule, providing an additional high-speed port.This could be used, for example, to provide a FastEthernet or Asynchronous Transfer Mode (ATM)backbone connection to the rest of your network.Transceiver ModuleA slot at the rear of the unit allows you to installany of the 3Com 10Mbps Ethernet Transceiver Mod-ules. When a Transceiver Module is fitted, port 1automatically switches to become the TransceiverModule port. The Transceiver Module can provide a10Mbps link to the rest of your network.Backbone PortThe Switch allows you to specify any port to be abackbone port with the following attributes:n Frames with unknown addresses received by theSwitch are forwarded to the port.n Addresses received on the port are not stored inthe Switch Database (the database which con-tains the device addresses received by theSwitch).A backbone port is typically used to connect theSwitch to the backbone of large networks (over 500MAC addresses). For information about how tospecify a backbone port for a new or initializedSwitch, refer to “Setting Up the Switch Unit” onpage 4-9.You can specify one backbone port for each VLANdefined on the Switch. For more information abouthow to specify a backbone port for a VLAN, refer to“Setting Up VLANs on the Switch” on page 5-8.
