Cisco Catalyst 2000 Configuration Handbook page 79

58 Cisco LAN Switching Configuration Handbook
autonegotiate the speed). The speeds of 10BASE-T, 100FX, Gigabit Interface
Converter (GBIC), and Small Form-factor Pluggable (SFP) ports are fixed and cannot
be set with this command.
Tip Choosing the auto speed for a port (the default) enables the port to participate in a
negotiation with the far end of the link. The two endpoints exchange information about
their capabilities and choose the best speed and duplex mode supported by both. If one
endpoint of a link has autonegotiation disabled, however, the other endpoint can only
sense the link speed from the electrical signals. The duplex mode can't be determined and
is left to the current default mode.
If you need to set the speed and duplex mode of the switch port to something other than
auto, be sure to set the device at the far end of the link to the same values.
Generally, if a 10/100/1000BASE-T switch port connects to another similar switch port or
to a mission-critical device such as a server, router, or firewall, you should set the speed
and duplex to a fixed value. By so doing, you eliminate any possibility of autonegotiation
forcing the port to a lower speed in the future.
(Optional) Set the port duplex mode:
3.
(interface) duplex {full | half | auto}
You can set the duplex mode to one of full. The auto option is not available on the
Catalyst 6500 IOS; if the speed is set to auto, the duplex follows suit.
Tip The duplex mode can be autonegotiated only if the port speed is also set to auto (or
autonegotiate). The 10/100 Ethernet ports can be set to either full- or half-duplex. Beware
of a port that has a duplex mismatch, in which one end is full- and the other is half-duplex.
This condition can cause a poor response and a high error rate. Make sure that both ends
of a link are set to autonegotiate or the same duplex setting. Although Cisco devices sup-
port only full-duplex, the IEEE 802.3z standard does have support for half-duplex
GigabitEthernet. Because of this, duplex is negotiated between GigabitEthernet devices.
(Optional) Set the port traffic flow control:
4.
(interface) flowcontrol {send | receive} {desired | off | on}
A switch port can receive pause frames, causing transmission to stop for a short
time while buffers at the far end are full. By default, receive processing is off for all
switch port types (except 10 Gigabit Ethernet). A port can also send pause frames if
its buffers are full. By default, send is on for Fast Ethernet, desired for Gigabit, and
off for all other port types. The desired keyword is available for Gigabit ports only,
where autonegotiation is inherent.
(Optional) Control port negotiation:
5.
(interface) [no] negotiation auto