Cisco Show Interface Reference

a04.irvnca01.us.ra#sh int Serial3/0/23:0                               
Serial3/0/23:0 is up, line protocol is up                              
  Hardware is PA-MC-2T3+                                                 
  Description: SDA Freight Data Corporation T1 CIR/CT3 (sdafda)75hcre000944-001 
  Internet address is 207.199.99.137/30                                       
  MTU 1500 bytes, BW 256 Kbit, DLY 20000 usec, rely 255/255, load 1/255         
  Encapsulation PPP, crc 16, loopback not set                                   
  Keepalive set (10 sec)                                                        
  LCP Open                                                                      
  Open: IPCP, CDPCP                                                             
  Last input 00:00:03, output 00:01:08, output hang never                       
  Last clearing of "show interface" counters never                        
  Input queue: 0/75/0 (size/max/drops); Total output drops: 0                 
  Queueing strategy: weighted fair                                            
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/1/256 (active/max active/max total)                     
     Reserved Conversations 0/0 (allocated/max allocated)                  
  5 minute input rate 0 bits/sec, 0 packets/sec                               
  5 minute output rate 0 bits/sec, 0 packets/sec                                
     20950 packets input, 1992090 bytes, 0 no buffer                            
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles                      
     1 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 1 abort              
     31524 packets output, 10804297 bytes, 0 underruns                          
     0 output errors, 0 collisions, 0 interface resets                          
     0 output buffer failures, 0 output buffers swapped out               
     0 carrier transitions no alarm present                                   
  Timeslot(s) Used: 1-4, subrate: 256Kb/s, transmit delay is 0 flags          
  non-inverted data

Interface and Line Protocol Status

Line State Possible Causes and Actions
Serial x is up, line protocol is up This status indicates that the interface is functioning properly
Serial x is down, line protocol is down This status indicates that the router is not sensing a carrier detect (CD) signal.

Possible Causes:
  1. Telephone company problem.
  2. Faulty or incorrect cabling
  3. Hardware failure
Suggested Actions:
  1. Check the LED's on the CSU/DSU to see if the CD light is active.
  2. Verify that the cables are connected properly.
  3. Reset your equipment
  4. Contact your leased-line provider
  5. Replace faulty equipment
Serial x is up, line protocol is down Possible Causes:
  1. Local or remote router misconfigured
  2. Keep-alives not being sent by remote router
  3. Leased-line or other carrier service problems, such as noisy lines or faulty switch
  4. Timing problem on cable, possibly caused by the CSU/DSU not being set correctly.
  5. Failed local or remote CSU/DSU.
  6. Router failure.
Serial x is up, line protocol is up (looped) Possible Causes:
  1. Loop exists in the circuit. Contact your leased line provider or owner of remote router to remove loop.
Serial x is administratively down, line protocol is down. Possible Causes:
  1. Router configuration includes the shutdown interface configuration command.
  2. Duplicate IP address.

Hardware

This field describes the type of hardware that the interface is connected to. In this case, this Serial interface is part of a channelized T3.

Description

This field is simply used to describe the interface by the network administrator. It has not bearing on connectivity.

Internet address

This is the IP address and subnet mask assigned to the interface in question. In this case, the IP address is 207.199.99.137 and it has a subnet mask of 255.255.255.252.

MTU, BW, DLY, rely, and load

  • MTU - Maximum Tranmission Unit. By default, this is 1500 bytes, which describes the largest packet that can be sent through the interface before the packet is fragmented.
  • BW - Bandwidth. This field is defined by the network administrator and has no actual effect on the bandwidth of a line. It is simply used for describing the load on a specific interface.
  • DLY - Delay. Amount of micro seconds of delay. I do not have any more information on this at this time.
  • rely - Reliability. Reliability of the interface as a fraction of 255 (255/255 is 100% reliability), calculated as an exponential average over five minutes (default).
  • load - Load Average. Load on the interface as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average over five minutes (default).

Encapsulation and Loopback

  • Encapsulation is the type of Data-Link encapsulation. This is commonly either PPP, HDLC (Cisco's proprietary PPP), Frame-Relay, and ATM.
  • Loopback specifies whether the loopback bit is set in the D channel signalling.

Last input

  • The last input is the number of hours, minutes, and seconds since the last packet was successfully received by an interface. This is useful for determining when a dead interface.
  • The last output is the number of hours, minutes, and seconds since the last packet was successfully transmitted by an interface. This is useful for determining when a dead interface failed.
  • The output hang is the number of hours, minutes, and seconds (or never) since the interface was last reset because of a transmission that took too long.

Last clearing

This shows the elapsed time, in seconds, since the last clearing of the interface counters that will be described in a later section on counters.

Output queue, input queue, drops

Number of packets in output and input queues. Each number is followed by a slash, the maximum size of the queue, and the number of packets dropped due to a full queue. Output drops can be caused when the output media cannot accept frames and the output queue reaches the maximum value before it starts dropping packets. Output drops may not necessarily indicate a problem since an explorer frame being dropped because it has already traveled on a particular ring can increment the output drops counter. Increasing input drops on the other hand, can be serious and should be looked into carefully. Input drops can be caused by insufficient system buffers - see 0 no buffer in the show interfaces tokenRing 0 output above. The incrementing no buffer counter of the show interfaces output may correlate to the incrementing misses counter of the show buffers output, and the appropriate buffer pool may need to be tuned.

5 minute input/output rate

Average number of bits and packets received and transmitted per second in the last five minutes.

Counters

  • Packets input - Total number of error-free packets received.
  • Broadcasts - Total number of broadcast or multicast packets received.
  • Runts - Number of packets discarded because they are smaller than the medium's minimum packet size.
  • Giants - Number of packets that are discarded because they exceed the medium's maximum packet size.
  • Throttle - This counter indicates the number of times the input buffers of an interface have been cleaned because they have not been serviced fast enough or they are overwhelmed. Typically, an explorer storm can cause the throttles counter to increment. It's important to note that every time you have a throttle, all the packets in the input queue get dropped. This causes very slow performance and may also disrupt existing sessions.
  • Parity - Number of parity errors on the HSSI.
  • RX Disabled - Indicates inability to get a buffer when accessing a packet.
  • Input Errors - Sum of all errors that prevented the receipt of datagrams. This may not balance with the sum of the enumerated output errors, because some datagrams may have more than one error and others may have errors that do not fall into any of the specific categories.
  • CRC - Cyclic redundancy checksum generated mismatch. CRC errors also are reported when a far-end abort occurs and when the idle flag pattern is corrupted. This makes it possible to get CRC errors even when there is no data traffic.
  • Frame - Number of packets received incorrectly having a CRC error and a noninteger number of octets.
  • Overrun - Number of times the serial receiver hardware was unable to hand received data to a hardware buffer because the input rate exceeded the receiver's ability to handle the data.
  • Ignored - Number of received packets ignored by the interface because the interface hardware ran low on internal buffers.
  • Abort - Number of packets whose receipt was aborted.
  • Bytes - Total number of bytes, including data and MAC encapsulation, transmitted by the system.
  • Underruns - Number of times that the far-end router's transmitter has been running faster than the near-end router's receiver can handle. This may never happen (be reported) on some interfaces.
  • Congestion Drop - Number of messages discarded because the output queue on an interface grew too long.
  • Output Errors - Sum of all errors that prevented the final transmission. This may not balance with the sum of the enumerated output errors, because some datagrams may have more than one error and others may have errors that do not fall into any of the specific categories.
  • Interface Resets - Number of times an interface has been completely reset.
  • Restarts - Number of times the controller was restarted because of errors.
  • Carrier Transitions - Number of times the carrier detect signal of a serial interface has changed state.
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