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Document No. 650-100-700, Issue 1 23-7
Using RMON and Ethernet Statistics to Analyze Network Performance
CLI Command
To view network statistics using the CLI, enter the following command in
Privileged mode:
(configure)#
show ethernet counters <cr | mod-num | mod-swport-
spec>
Setting Up Port Mirroring
Configuring an RMON mirror port allows you to mirror traffic from a port
or set of ports to a specific mirror port, where you can attach a sniffer or
RMON probe. The switch supports a single mirror port and a single source
port for each switch fabric port. For example, 20-port Fast Ethernet cards
have two fabric ports (one for ports 1 through 10, one for ports 11 through
20). You can set up a single source port and a single mirror port for each set
of ports associated with a fabric port. You can also choose to mirror all
traffic from a particular fabric port to the mirror port, or set up multiple
source ports to mirror traffic to a single mirror port.
Collisions (half-
duplex links only) Counts number of times that packets
have collided on the network.
Collisions increase as network use of
shared segments increases. Therefore,
if the collision rate increases without
an increase of network use, it might
indicate a problem. Guidelines for
appropriate collision rates are:
• 10 percent: Normal collision rate
for shared Ethernet segment.
• 30 percent: Collisions begin to
interfere with performance.
• 70 percent: Practical limit for
network to remain functioning.
A full-duplex link should not show
collision activity. Collisions are rare in
a switched network, unless your
switched segments attach to multiple
ends stations (a legal configuration
option).
Collisions do not occur on fiber optic
cable and thus do not occur on the 10-
Gigabit module.
Possible causes:
• Busy network
• Broken adapter (not listening before
broadcasting)
• Network loop
Possible actions (respectively):
• If you have multiple stations on a
switch segment, reconfigure network
into segments with fewer stations.
• Isolate each adapter to see if the
problem ceases.
• Activate spanning tree to resolve loops
automatically.
• Ensure that there are no connections to
the same station where both
connections are simultaneously
active.
Table 23-1. Ethernet Interface Statistics Web Page Fields
Statistic Indicates Actions
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