Information Technology Reference
In-Depth Information
Copper
Make sure that you have the correct cable for the type of connection you are making. Category 3 cable
can be used for 10 MB UTP connections, but Category 5 should be used for 10/100 connections.
A straight-through RJ-45 cable is used for end stations, routers, or servers to connect to a switch or hub.
An Ethernet crossover cable is used for switch-to-switch or hub-to-switch connections. Below is the
pin-out for an Ethernet crossover cable. Maximum distances for Ethernet or Fast Ethernet copper wires
are 100 meters. A good general rule of thumb is that when crossing an OSI layer, such as between a
switch and a router, use a straight-through cable; when connecting two devices in the same OSI layer,
such as between two routers or two switches, use a crossover cable. For purposes of this rule only, treat
a workstation like a router.
Figure 23-1 shows the pinouts required for a switch-to-switch crossover cable.
Figure23-1 Illustration of the Pinouts Required for a Switch-to-Switch Crossover Cable
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Hub
3 TD+
6 TD-
Hub
3 TD+
6 TD-
1 RD+
2 RD-
1 RD+
2 RD-
Fiber
For fiber, make sure that you have the correct cable for the distances involved and the type of fiber ports
being used (single mode, multimode). Make sure that the ports being connected are both single-mode or
both multimode ports. Single-mode fiber generally reaches 10 km, and multimode fiber can usually reach
2 km, but the special case of 100BaseFX multimode used in half-duplex mode can go only 400 meters.
For fiber connections, make sure that the transmit lead of one port is connected to the receive lead of the
other port, and vice versa; transmit-to-transmit and receive-to-receive will not work.
For gigabit connections, GBICs must be matched on each side of the connection. There are different
types of GBICs, depending on the cable and distances involved: short wavelength (SX), long
wavelength/long haul (LX/LH), and extended distance (ZX). An SX GBIC needs to connect with an SX
GBIC; an SX GBIC will not link with an LX GBIC. Also, some gigabit connections require conditioning
cables, depending on the lengths involved. Refer to the GBIC installation notes (for examples, see
www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/cnfg_nts/ethernet/5399_01.htm).
If your gigabit link will not come up, check to make sure that the flow control and port negotiation
settings are consistent on both sides of the link. There could be incompatibilities in the implementation
of these features if the switches being connected are from different vendors. If in doubt, turn off these
features on both switches.
