Chapter 4 Troubleshooting
Diagnosing Problems
4-6
Catalyst 3750 Switch Hardware Installation Guide
78-15136-03
No connectivity Incorrect or bad cable
These are results of no link at both
ends:
• A crossover cable was used
when a straight-through was
required, or vice-versa.
• The cable is wired incorrectly.
• A crossover or straight-through
cable is wired incorrectly.
• STP checking for possible
loops.
• For the correct pinouts and
the proper application of
crossover vs.
straight-through cables, see
the “Two Twisted-Pair
Cable Pinouts” section on
page B-5.
• Enable the automatic
medium-dependent-
interface crossover
(Auto-MDIX) feature.
Note Many legacy powered
devices, including older
Cisco IP phones and
access points that do not
fully support IEEE
802.3af, might not
support PoE when
connected to the
switches by a crossover
cable.
• Replace with a tested good
cable.
• For 1000BASE-T
connections, be sure to use
a twisted four-pair,
Category 5 cable.
• Wait 30 seconds for the port
LED to turn green.
Table 4-1 Common Problems and Solutions (continued)
Symptom Possible Cause Resolution
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