Troubleshooting Guide

1
A duplex mismatch can result in performance issues, intermittent connectivity, and loss of
communication. When you troubleshoot NIC issues, verify that the NIC and switch use a valid
configuration.
2
Some third-party NIC cards can fall back to half-duplex operation mode, even though both the switchport
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
100 Mbps, Full-
duplex
AUTO
100 Mbps, Full-
duplex
100 Mbps,
Half-duplex
Duplex
Mismatch
1
AUTO
100 Mbps, Full-
duplex
100 Mbps,
Half-duplex
100 Mbps, Full-
duplex
Duplex
Mismatch
1
100 Mbps, Full-
duplex
100 Mbps, Full-
duplex
100 Mbps, Full-
duplex
100 Mbps, Full-
duplex
Correct
Manual
Configuration
2
100 Mbps, Half-
duplex
AUTO
100 Mbps,
Half-duplex
100 Mbps,
Half-duplex
Link is
established, but
switch does not
see any
autonegotiation
information
from NIC and
defaults to half-
duplex when
operating at
10/100 Mbps.
10 Mbps, Half-
duplex
AUTO
10 Mbps, Half-
duplex
10 Mbps, Half-
duplex
Link is
established, but
switch does not
see Fast Link
Pulse (FLP)
and defaults to
10 Mbps half-
duplex.
10 Mbps, Half-
duplex
100 Mbps, Half-
duplex
No Link No Link
Neither side
establishes
link, due to
speed
mismatch.
AUTO
100 Mbps, Half-
duplex
100 Mbps,
Half-duplex
100 Mbps,
Half-duplex
Link is
established, but
NIC does not
see any
autonegotiation
information and
defaults to 100
Mbps, half-
duplex.
AUTO
10 Mbps, Half-
duplex
10 Mbps, Half-
duplex
10 Mbps, Half-
duplex
Link is
established, but
NIC does not
see FLP and
defaults to 10
Mbps, half-
duplex.