cisco hands-on experience


switchport/interface – troubleshoot sh int counters error

It is useful to get familiar with the ‘sh int counters’ command, to check if the switchport/interface
(switchport-interface) generate failure on the physical or data link layer.
In some cases clients has latencies or packet loss and therefore bad network performance.
In this blog i want to explain to perform the right outputs and contrue for the troubleshooing.

This will be done with the counter command.

In general you can use the ‘sh interface counters’ for the whole device.
The output show.

You get information of all ports fo the device.
I see how many traffic is generated on each port.

sh int counters
Lab_2960#sh int counters

Port            InOctets    InUcastPkts    InMcastPkts    InBcastPkts
Fa0/1         2607782237       20575978             64           8269
Fa0/2         2512563028       25019118             68           8392
Fa0/3         6566347115       46165305             70           8544
Fa0/4          122927612        1854840            166           3946
Fa0/5         3852466744       31035707             70           8680
Fa0/6         3366037701       30759822            126           9872
Fa0/7         2669734749       23264365             64           8867
Fa0/8         6929619323       51960802             68          14237
Fa0/9         5333231843       45767428           1050          27094
Fa0/10        7820789313       59365097             66           8882
Fa0/11        5229745076       32723963             66          13763
Fa0/12        2811031585       24056443             64           8714
Fa0/13        6718742880       49043343             70           8971
Fa0/14        7455778844       54001180             70           8494
Fa0/15        5295191877       35160413             70          14175
Fa0/16        5099384255       35059792              4           1428
Fa0/17        6933775606       46558177             66           8857
Fa0/18                 0              0              0              0
Fa0/19                 0              0              0              0
Fa0/20                 0              0              0              0
Fa0/21                 0              0              0              0
Fa0/22                 0              0              0              0
Fa0/23                 0              0              0              0
Fa0/24                 0              0              0              0
Gi0/1        93568911942      500246610       59033992        8954303
Gi0/2         4546637819        6313463       40181854        3636990
Po1          98115539371      506560072       99215757       12591291

Port           OutOctets   OutUcastPkts   OutMcastPkts   OutBcastPkts
Fa0/1         6838349621       22548464       35031112       12499576
Fa0/2         6341266762       23615997       35031148       12499678
Fa0/3        11366436026       45446811       35031149       12499379
Fa0/4         5986112931        9533380       35020235       12501507
Fa0/5         7991854885       30203129       35031134       12499215
Fa0/6         7589038814       30125170       35031552       12498719
Fa0/7         8979447885       27160646       35031110       12499272
Fa0/8        11407978306       48627780       35031121       12496184
Fa0/9        13047575247       47678808       35030766       12482057
Fa0/10       12045478321       52869385       35031113       12499094
Fa0/11        9693549501       34887975       35031112       12496515
Fa0/12        7350337843       24775514       35031109       12499109
Fa0/13       10797432851       45182797       35031140       12498906
Fa0/14       11540436434       49413080       35031144       12499327
Fa0/15        9534640335       35830007       35031142       12496333
Fa0/16        9556586823       35722812       35030689       12506359
Fa0/17       11384570127       44956315       35031110       12499007
Fa0/18                 0              0              0              0
Fa0/19                 0              0              0              0
Fa0/20                 0              0              0              0
Fa0/21                 0              0              0              0
Fa0/22                 0              0              0              0
Fa0/23                 0              0              0              0
Fa0/24                 0              0              0              0
Gi0/1        41089646251      359947539        2416085          79807
Gi0/2        40727909521      251235635        2415428          77102
Po1          81817545776      611183172        4831430         156909

Now i want to know the error packets on dedicated ports.
I only have some Xmit-Err on Pa0/10.

error packets
Lab_2960#sh int counters errors

Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err  UnderSize  OutDiscards
Fa0/1               0           0           0           0          0            0
Fa0/2               0           0           0           0          0            0
Fa0/3               0           0           0           0          0            0
Fa0/4               0           0           0           0          0            0
Fa0/5               0           0           0           0          0            0
Fa0/6               0           0           0           0          0            0
Fa0/7               0           0           0           0          0            0
Fa0/8               0           0           0           0          0            0
Fa0/9               0           0           0           0          0            0
Fa0/10              0           0           0           1          0            0
Fa0/11              0           0           0           0          0            0
Fa0/12              0           0           0           0          0            0
Fa0/13              0           0           0           0          0            0
Fa0/14              0           0           0           0          0            0
Fa0/15              0           0           0           0          0            0
Fa0/16              0           0           0           0          0            0
Fa0/17              0           0           0           0          0            0
Fa0/18              0           0           0           0          0            0
Fa0/19              0           0           0           0          0            0
Fa0/20              0           0           0           0          0            0
Fa0/21              0           0           0           0          0            0
Fa0/22              0           0           0           0          0            0
Fa0/23              0           0           0           0          0            0
Fa0/24              0           0           0           0          0            0
Gi0/1               0           0           0           0          0            0
Gi0/2               0           0           0           0          0            0
Po1                 0           0           0           0          0            0

Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen      Runts     Giants
Fa0/1              0          0          0           0          0          0          0
Fa0/2              0          0          0           0          0          0          0
Fa0/3              0          0          0           0          0          0          0
Fa0/4              0          0          0           0          0          0          0
Fa0/5              0          0          0           0          0          0          0
Fa0/6              0          0          0           0          0          0          0
Fa0/7              0          0          0           0          0          0          0

Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen      Runts     Giants
Fa0/8              0          0          0           0          0          0          0
Fa0/9              0          0          0           0          0          0          0
Fa0/10             0          0          0           0          0          0          0
Fa0/11             0          0          0           0          0          0          0
Fa0/12             0          0          0           0          0          0          0
Fa0/13             0          0          0           0          0          0          0
Fa0/14             0          0          0           0          0          0          0
Fa0/15             0          0          0           0          0          0          0
Fa0/16             0          0          0           0          0          0          0
Fa0/17             0          0          0           0          0          0          0
Fa0/18             0          0          0           0          0          0          0
Fa0/19             0          0          0           0          0          0          0
Fa0/20             0          0          0           0          0          0          0
Fa0/21             0          0          0           0          0          0          0
Fa0/22             0          0          0           0          0          0          0
Fa0/23             0          0          0           0          0          0          0
Fa0/24             0          0          0           0          0          0          0
Gi0/1              0          0          0           0          0          0          0
Gi0/2              0          0          0           0          0          0          0
Po1                0          0          0           0          0          0          0

I want only to see a special error port.

one port only
Lab_2960# sh int fa0/10 counters err

Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err  UnderSize  OutDiscards
Fa0/10              0           0           0           1          0            0

Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen      Runts     Giants
Fa0/10             0          0          0           0          0          0          0

To see a deeper error output use the command ‘sh controllers ethernet-controller fa0/10

sh controllers ethernet-controller fa0/10
Lab_2960#sh controllers ethernet-controller fa0/10

Transmit FastEthernet0/10                Receive
3455860490 Bytes                       3525850293 Bytes
52869960 Unicast frames                59365274 Unicast frames
35034035 Multicast frames                    66 Multicast frames
12499585 Broadcast frames                  8882 Broadcast frames
0 Too old frames              3436368828 Unicast bytes
0 Deferred frames                   4224 Multicast bytes
0 MTU exceeded frames             699213 Broadcast bytes
0 1 collision frames                   0 Alignment errors
0 2 collision frames                   0 FCS errors
0 3 collision frames                   0 Oversize frames
0 4 collision frames                   0 Undersize frames
0 5 collision frames                   0 Collision fragments
0 6 collision frames
0 7 collision frames                5183 Minimum size frames
0 8 collision frames            37825242 65 to 127 byte frames
0 9 collision frames            21540658 128 to 255 byte frames
0 10 collision frames               2624 256 to 511 byte frames
0 11 collision frames                516 512 to 1023 byte frames
0 12 collision frames                  0 1024 to 1518 byte frames
0 13 collision frames                  0 Overrun frames
0 14 collision frames                  0 Pause frames
0 15 collision frames
0 Excessive collisions                 1 Symbol error frames
0 Late collisions                      0 Invalid frames, too large
0 VLAN discard frames                  0 Valid frames, too large
0 Excess defer frames                  0 Invalid frames, too small
10459768 64 byte frames                       0 Valid frames, too small
63512687 127 byte frames
22801071 255 byte frames                      0 Too old frames
1692680 511 byte frames                      0 Valid oversize frames
1934766 1023 byte frames                     0 System FCS error frames
2608 1518 byte frames                     0 RxPortFifoFull drop frame
0 Too large frames
0 Good (1 coll) frames
0 Good (>1 coll) frames

How to clear the frames for special swithports?

clear counters
Lab_2960#clear counters fa0/10
Clear “show interface” counters on this interface [confirm]

You want to clear the counters on the controllers?
no confirmation is needed

clear controllers
Lab_2960#clear controllers ethernet-controller fa0/10

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.

SOURCE

  1. Andrey Reply

    Awesome you should think of sonihtemg like that

    • George Reply

      Good to hear from you

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  3. bingo Reply

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