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Chapter 2

Connecting the Switch Block

it doesn't share bandwidth with any other devices. Frames sent by two nodes
cannot collide because there are physically separate transmit and receive cir-
cuits between the nodes.

Use Full-Duplex Ethernet in the Distribution Layer

Because users typically use client/server applications using read/write asym-
metrical traffic, the best performance for full-duplex would be in the distri-
bution layer, not necessarily in the access layer.

Full-Duplex with Flow Control was created to avoid packets being

dropped if the buffers on an interface fill up before all packets can be pro-
cessed. However, some vendors might not interoperate, and the buffering
might have to be handled by upper-layer protocols instead.

Auto-Negotiation

Auto-negotiation is a process that allows clients and switches to agree on a
link capability. This is used to determine the link speed as well as the duplex
being used. The auto-negotiation process uses priorities to set the link con-
figuration. Obviously, if both a client and switch port can use 100Mbps, full-
duplex connectivity, that would be the highest-priority ranking, whereas
half-duplex, 10Mbps Ethernet is the lowest ranking.

You need to understand that the auto-negotiation protocols do not work

that well and you would be better off to configure the switch and NICs to
run in a dedicated mode instead of letting the clients and switches auto-
negotiate. Later in this chapter, we'll show you how to configure your
switches with both the speed and duplex options.

Distance

FastEthernet does have some drawbacks. It uses the same singing techniques
as 10Mbps Ethernet, so it has the same distance constraints. In addition,
10Mbps Ethernet can use up to four repeaters, whereas FastEthernet can use
only one or two, depending on the type of repeater. Table 2.1 shows a com-
parison of FastEthernet technologies.

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