Lucent Technologies Cajun P220, Operation Manual

Page: 279 / 335

Analyzing Network Performance Using RMON and Ethernet Statistics (Layer 2 & Layer 3)
Cajun P550/P220 Switch Operation Guide 17 - 3
Multicasts Normal during network operation.
For example, multicast packets are
to send target video streams to
selected stations on the network,
and are part of the operation of the
Spanning Tree Protocol. Possible causes:
• Too many multicast frames can
consume valuable network
bandwidth.
Possible actions:
• Using Intelligent Multicasting
can significantly reduce
multicast traffic on individual
ports.
• Segmenting the network into
smaller VLANs and routing
between them can also help
control proliferation of
multicasts.
CRC (Cyclic
Redundancy
Check) or
Alignment
Errors Counts of the number of times that
the number of bits in a frame
cannot be divided by 8 (that is,
cannot be broken into legal octets),
and that contain a Frame Check
Sequence validation error. Typically
caused by turning equipment on or
off, and by noise on twisted pair
segments. These errors can also
result from configuring a network
that does not comply with 802.3
standards. In a standards-compliant
Ethernet network, CRC or
alignment errors represent transit
and receive bit errors.
The Ethernet standard allows 1 in
10
8
bit error rate, but you should
expect performance to be less than
1 in 10
12
packets. Rates in excess of
one error per one thousand packets
indicate a serious problem.
Possible causes:
• Defect at the transmitting
station.
• Turning equipment on or off.
This should cause only a few
errors.
• Damaged cables.
• Interference on network
cabling.
Possible actions (respectively):
• Use port error statistics to
isolate the problem. Check the
transceiver or adapter card
connected to the port where
the problem seems to
originate. Also check the cable
and cable connections for
damage.
• Normal operation, no action
required.
• Check cables for damage.
• Inspect cable runs to see if they
are too close to noisy devices,
and check for problems with
network devices.
Table 17-1. Interpreting Ethernet Interface Statistics (Continued)
Statistic Indicates Actions