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performance−related issues. The most common problems with NIC issues deal with speed and duplex
configuration. Table 1 summarizes all possible settings of speed and duplex for FastEthernet NICs and switch
ports.
Note: This section is only applicable for 10/100/1000 Mbps (1000BASE−T) NICs, and not 1000BASE−X
NICs.
Table 1Autonegotiation Valid Configuration
Configuration
NIC
(Speed/Duplex)
Configuration
Switch
(Speed/Duplex)
Resulting NIC
Speed/Duplex
Resulting
Catalyst
Speed/Duplex
Comments
AUTO
AUTO
1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
Assuming
maximum
capability of
Catalyst switch,
and NIC is
1000 Mbps,
full−duplex.
1000 Mbps,
Full−duplex
AUTO
1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
Link is
established, but
the switch does
not see any
autonegotiation
information
from NIC.
Since Catalyst
switches
support only
full−duplex
operation with
1000 Mbps,
they default to
full−duplex,
and this
happens only
when operating
at 1000 Mbps.
AUTO 1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
Assuming
maximum
capability of
NIC is 1000
Mbps,
full−duplex.
1000 Mbps,
Full−duplex 1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
1000 Mbps,
Full−duplex
Correct Manual
Configuration
100 Mbps,
Full−duplex 1000 Mbps,
Full−duplex
No Link No Link
Neither side
establishes link,
due to speed
mismatch
AUTO