switchport/interface – troubleshoot sh int counters error

In the following table you see descriptions and causes of error counters

Counters (in alphabetical order) Description and Common Causes of Incrementing Error Counters
Align-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. Alignment errors are a count of the number of frames received that don’t end with an even number of octets and have a bad Cyclic Redundancy Check (CRC). Common Causes: These are usually the result of a duplex mismatch or a physical problem (such as cabling, a bad port, or a bad NIC). When the cable is first connected to the port, some of these errors can occur. Also, if there is a hub connected to the port, collisions between other devices on the hub can cause these errors. Platform Exceptions: Alignment errors are not counted on the Catalyst 4000 Series Supervisor I (WS-X4012) or Supervisor II (WS-X4013).
babbles Description: Cisco IOS sh interfaces counter. CatOS counter indicating that the transmit jabber timer expired. A jabber is a frame longer than 1518 octets (which exclude framing bits, but include FCS octets), which does not end with an even number of octets (alignment error) or has a bad FCS error.
Carri-Sen Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The Carri-Sen (carrier sense) counter increments every time an Ethernet controller wants to send data on a half duplex connection. The controller senses the wire and checks if it is not busy before transmitting. Common Causes: This is normal on an half duplex Ethernet segment.
collisions Descriptions: Cisco IOS sh interfaces counter. The number of times a collision occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
CRC Description: Cisco IOS sh interfaces counter. This increments when the CRC generated by the originating LAN station or far-end device does not match the checksum calculated from the data received. Common Causes: This usually indicates noise or transmission problems on the LAN interface or the LAN itself. A high number of CRCs is usually the result of collisions but can also indicate a physical issue (such as cabling, bad interface or NIC) or a duplex mismatch.
deferred Description: Cisco IOS sh interfaces counter. The number of frames that have been transmitted successfully after they wait because the media was busy. Common Causes: This is usually seen in half duplex environments where the carrier is already in use when it tries to transmit a frame.
pause input Description: Cisco IOS show interfaces counter. An increment in pause input counter means that the connected device requests for a traffic pause when its receive buffer is almost full. Common Causes: This counter is incremented for informational purposes, since the switch accepts the frame. The pause packets stop when the connected device is able to receive the traffic.
input packetswith dribble condition Description: Cisco IOS sh interfaces counter. A dribble bit error indicates that a frame is slightly too long. Common Causes: This frame error counter is incremented for informational purposes, since the switch accepts the frame.
Excess-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. A count of frames for which transmission on a particular interface fails due to excessive collisions. An excessive collision happens when a packet has a collision 16 times in a row. The packet is then dropped. Common Causes: Excessive collisions are typically an indication that the load on the segment needs to be split across multiple segments but can also point to a duplex mismatch with the attached device. Collisions must not be seen on interfaces configured as full duplex.
FCS-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of valid size frames with Frame Check Sequence (FCS) errors but no framing errors. Common Causes: This is typically a physical issue (such as cabling, a bad port, or a bad Network Interface Card (NIC)) but can also indicate a duplex mismatch.
frame Description: Cisco IOS sh interfaces counter. The number of packets received incorrectly that has a CRC error and a non-integer number of octets (alignment error). Common Causes: This is usually the result of collisions or a physical problem (such as cabling, bad port or NIC) but can also indicate a duplex mismatch.
Giants Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. Frames received that exceed the maximum IEEE 802.3 frame size (1518 bytes for non-jumbo Ethernet) and have a bad Frame Check Sequence (FCS). Common Causes: In many cases, this is the result of a bad NIC. Try to find the offending device and remove it from the network. Platform Exceptions: Catalyst Cat4000 Series that run Cisco IOS Previous to software Version 12.1(19)EW, the giants counter incremented for a frame > 1518bytes. After 12.1(19)EW, a giant in show interfaces increments only when a frame is received >1518bytes with a bad FCS.
ignored Description: Cisco IOS sh interfaces counter. The number of received packets ignored by the interface because the interface hardware ran low on internal buffers. Common Causes: Broadcast storms and bursts of noise can cause the ignored count to be increased.
Input errors Description: Cisco IOS sh interfaces counter. Common Causes: This includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts. Other input-related errors can also cause the input errors count to be increased, and some datagrams can have more than one error. Therefore, this sum cannot balance with the sum of enumerated input error counts. Also refer to the section Input Errors on a Layer 3 Interface Connected to a Layer 2 Switchport.
Late-Col Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. The number of times a collision is detected on a particular interface late in the transmission process. For a 10 Mbit/s port this is later than 512 bit-times into the transmission of a packet. Five hundred and twelve bit-times corresponds to 51.2 microseconds on a 10 Mbit/s system. Common Causes: This error can indicate a duplex mismatch among other things. For the duplex mismatch scenario, the late collision is seen on the half duplex side. As the half duplex side is transmitting, the full duplex side does not wait its turn and transmits simultaneously which causes a late collision. Late collisions can also indicate an Ethernet cable or segment that is too long. Collisions must not be seen on interfaces configured as full duplex.
lost carrier Description: Cisco IOS sh interfaces counter. The number of times the carrier was lost in transmission. Common Causes: Check for a bad cable. Check the physical connection on both sides.
Multi-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of times multiple collisions occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
no buffer Description: Cisco IOS sh interfaces counter. The number of received packets discarded because there is no buffer space. Common Causes: Compare with ignored count. Broadcast storms can often be responsible for these events.
no carrier Description: Cisco IOS sh interfaces counter. The number of times the carrier was not present in the transmission. Common Causes: Check for a bad cable. Check the physical connection on both sides.
Out-Discard Description: The number of outbound packets chosen to be discarded even though no errors have been detected. Common Causes: One possible reason to discard such a packet can be to free up buffer space.
output buffer failuresoutput buffers swapped out Description: Cisco IOS sh interfaces counter. The number of failed buffers and the number of buffers swapped out. Common Causes: A port buffers the packets to the Tx buffer when the rate of traffic switched to the port is high and it cannot handle the amount of traffic. The port starts to drop the packets when the Tx buffer is full and thus increases the underruns and the output buffer failure counters. The increase in the output buffer failure counters can be a sign that the ports are run at an inferior speed and/or duplex, or there is too much traffic that goes through the port. As an example, consider a scenario where a 1gig multicast stream is forwarded to 24 100 Mbps ports. If an egress interface is over-subscribed, it is normal to see output buffer failures that increment along with Out-Discards. For troubleshooting information, see the Deferred Frames (Out-Lost or Out-Discard) section of this document.
output errors Description: Cisco IOS sh interfaces counter. The sum of all errors that prevented the final transmission of datagrams out of the interface. Common Cause: This issue is due to the low Output Queue size.
overrun Description: The number of times the receiver hardware was unable to hand received data to a hardware buffer. Common Cause: The input rate of traffic exceeded the ability of the receiver to handle the data.
packets input/output Description: Cisco IOS sh interfaces counter. The total error free packets received and transmitted on the interface. Monitoring these counters for increments is useful to determine whether traffic flows properly through the interface. The bytes counter includes both the data and MAC encapsulation in the error free packets received and transmitted by the system.
Rcv-Err Description: CatOS show port or show port counters and Cisco IOS (for the Catalyst 6000 Series only) sh interfaces counters error. Common Causes: See Platform Exceptions. Platform Exceptions: Catalyst 5000 Series rcv-err = receive buffer failures. For example, a runt, giant, or an FCS-Err does not increment the rcv-err counter. The rcv-err counter on a 5K only increments as a result of excessive traffic. On Catalyst 4000 Series rcv-err = the sum of all receive errors, which means, in contrast to the Catalyst 5000, that the rcv-err counter increments when the interface receives an error like a runt, giant or FCS-Err.
Runts Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. The frames received that are smaller than the minimum IEEE 802.3 frame size (64 bytes for Ethernet), and with a bad CRC. Common Causes: This can be caused by a duplex mismatch and physical problems, such as a bad cable, port, or NIC on the attached device. Platform Exceptions: Catalyst 4000 Series that run Cisco IOS Previous to software Version 12.1(19)EW, a runt = undersize. Undersize = frame < 64bytes. The runt counter only incremented when a frame less than 64 bytes was received. After 12.1(19EW, a runt = a fragment. A fragment is a frame < 64 bytes but with a bad CRC. The result is the runt counter now increments in show interfaces, along with the fragments counter in show interfaces counters errors when a frame <64 bytes with a bad CRC is received. Cisco Catalyst 3750 Series Switches In releases prior to Cisco IOS 12.1(19)EA1, when dot1q is used on the trunk interface on the Catalyst 3750, runts can be seen on show interfaces output because valid dot1q encapsulated packets, which are 61 to 64 bytes and include the q-tag, are counted by the Catalyst 3750 as undersized frames, even though these packets are forwarded correctly. In addition, these packets are not reported in the appropriate category (unicast, multicast, or broadcast) in receive statistics. This issue is resolved in Cisco IOS release 12.1(19)EA1 or 12.2(18)SE or later.
Single-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of times one collision occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
throttles Description: Cisco IOS show interfaces. The number of times the receiver on the port is disabled, possibly because of buffer or processor overload. If an asterisk (*) appears after the throttles counter value, it means that the interface is throttled at the time the command is run. Common Causes: Packets which can increase the processor overload include IP packets with options, expired TTL, non-ARPA encapsulation, fragmentation, tunelling, ICMP packets, packets with MTU checksum failure, RPF failure, IP checksum and length errors.
underruns Description: The number of times that the transmitter has been that run faster than the switch can handle. Common Causes: This can occur in a high throughput situation where an interface is hit with a high volume of bursty traffic from many other interfaces all at once. Interface resets can occur along with the underruns.
Undersize Description: CatOS sh port and Cisco IOS sh interfaces counters errors . The frames received that are smaller than the minimum IEEE 802.3 frame size of 64 bytes (which excludes framing bits, but includes FCS octets) that are otherwise well formed. Common Causes: Check the device that sends out these frames.
Xmit-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. This is an indication that the internal send (Tx) buffer is full. Common Causes: A common cause of Xmit-Err can be traffic from a high bandwidth link that is switched to a lower bandwidth link, or traffic from multiple inbound links that are switched to a single outbound link. For example, if a large amount of bursty traffic comes in on a gigabit interface and is switched out to a 100Mbps interface, this can cause Xmit-Err to increment on the 100Mbps interface. This is because the output buffer of the interface is overwhelmed by the excess traffic due to the speed mismatch between the inbound and outbound bandwidths.

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