Troubleshooting Guide

Table 3—Possible Causes for Incrementing CatOS Counters
UnderSize
These are frames that are smaller than 64 bytes,
which includes FCS, and have a good FCS
value.
Single
Collisions
Single collisions are the number of times the
transmitting port had one collision before
successfully transmitting the frame to the media.
Multiple
Collisions
Multiple collisions are the number of times the
transmitting port had more than one collision
before successfully transmitting the frame to the
media.
Late
Collisions
A late collision occurs when two devices transmit
at the same time and neither side of the
connection detects a collision. The reason for
this occurrence is that the time to propagate the
signal from one end of the network to another is
longer than the time to put the entire packet on
the network. The two devices that cause the late
collision never see that the other sends until after
it puts the entire packet on the network. Late
collisions are detected by the transmitter after
the first time slot of the 64-byte transmit time
occurs. They are only detected during
transmissions of packets longer than 64 bytes.
Its detection is exactly the same as it is for a
normal collision; it just happens later than it does
for a normal collision.
Excessive
Collisions
Excessive collisions are the number of frames
that are dropped after 16 attempts to send the
packet resulted in 16 collisions.
Carrier
Sense
Carrier sense occurs every time an Ethernet
controller wants to send data and the counter is
incremented when there is an error in the
process.
Runts
These are frames smaller than 64 bytes with a
bad FCS value.
Giants
These are frames that are greater than 1518
bytes and have a bad FCS value.
Counter Description
Alignment
Errors
These are the result of collisions at half-duplex,
duplex mismatch, bad hardware (NIC, cable, or
port), or a connected device that generates
frames that do not end with on an octet and
have a bad FCS.
FCS
These are the result of collisions at half-duplex,
duplex mismatch, bad hardware (NIC, cable, or
port), or a connected device that generates
frames with bad FCS.
Xmit-Err
This is an indication of excessive input rates of
traffic. This is also an indication that the transmit
buffer is full. The counter must only increment in
situations in which the switch is unable to
forward out the port at a desired rate. Situations
such as excessive collisions and 10 Mb ports
cause the transmit buffer to become full. If you
increase speed and move the link partner to full-
duplex, it minimizes this occurrence.
Rcv-Err
This is an indication of excessive output rates of
traffic. This is also an indication that the receive
buffer is full. This counter must be zero unless
there is excessive traffic through the switch. In
some switches, the Out-Lost counter has a
direct correlation to the Rcv-Err.
UnderSize
This is an indication of a bad frame generated
by the connected device.
Single
Collisions
This is an indication of a half-duplex
configuration.
Multiple This is an indication of a half-duplex