Troubleshooting guide

Local Area Network
177
Any packet shorter than 64 bytes, but with a valid CRC, is considered a runt. A packet shorter
than 64 bytes, but with a bad CRC, is usually considered a fragment.
A packet that has a valid CRC, and is longer than 1518 bytes, is considered a long packet. A
packet that has a bad CRC and is longer than 1518 bytes is usually considered a jabber.
The following table can be used in conjunction with the L2 traffic counters to troubleshoot
network problems.
Table 60: Frame Length Errors
Counter Cause Corrective Action
RX Discards
Receive packets discarded.
Insufficient receive resources. Contact Mitel Technical Support.
RX CRC/FCS Errors
Packets received with CRC or
FCS errors.
Equipment powering up or down. No action.
Electrical noise on the LAN. Check for improper routing of ethernet
cables
Hardware fault on transmitting
device.
Replace faulty hardware.
Damaged/defective cable. Replace cable.
Bad cable termination at punch
down block or at RJ-45 or RJ-71
connector.
Repair cable termination.
Wiring plant is substandard For 10BaseT the wire should be Cat-3 or
better, for 100Base-T the wire should be
Cat-5 or better.
Duplex/speed mismatch. Check that setting on both ends of the
LAN segment are consistent.
Alignment Errors
Packets received with alignment
errors
See RX CRC/FCS Errors.
RX Symbol Errors
Valid length packets received that
had at least one invalid data
symbol.
See RX CRC/FCS Errors.
RX Fragments
Packet fragments received.
Fragments are pieces of a
packet. The packet is usually
fragmented due to a collision on
the LAN.
Collisions and fragments are normal in a
half-duplex network. Collisions and
fragments should be minimal or
non-existent in a full-duplex network.
RX Jabbers
A jabber is a packet that is longer
than 1518 bytes and has either a
FCS/CRC error or an alignment
error.
The jabber protection circuitry on
a network device has failed.
There is excessive electrical
noise on the LAN.
Replace the defective network device.
Check that the LAN cabling is correctly
installed—e.g., cables should not be
routed next to noise sources.
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