Monday, 30 April 2012

Cisco Show Interface Explained

Hi every one, I hope every one if fine and enjoying good Health, for last couple of weeks a lot of people asked me if I can explain each and every line of output from Cisco one important command when we start troubleshooting any thing which is 

Show interface  Gi0/10

Output from the command above is explained each output one by one. 
GigabitEthernet0/10 is up,

Indicates whether the interface hardware is currently active and if it has been taken down by an administrator. "Disabled" indicates the router has received errors in a keep alive interval and some time you have port security setup you will see error disbaled

line protocol is up (connected)

This indicates whether the software processes that handle the line protocol believe the interface is usable (that is, whether keepalives are successful)

Hardware is Gigabit Ethernet, address is 0022.0d50.2d32 (bia 0022.0d50.2d32)

Hardware type and Ethernet address.

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

Maximum Transmission Unit of the interface.
Bandwidth of the interface in kilobits per second.
Delay of the interface in microseconds.

 reliability 255/255, txload 1/255, rxload 1/255

Reliability of the interface 255/255 is 100% reliability , calculated on average over 5 minutes.
Load on the interface 255/255 is completely saturated link it is also calculated on average over 5 minutes

Encapsulation ARPA, loopback not set
Encapsulation method assigned to interface.

Keepalive not set
Indicates whether keepalives are set or not.

Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseSX SFP
Duplex setting of the interface if the interface is full Duplex , in the example above I have media type of SFP fiber interface module

ARP type: ARPA, ARP Timeout 04:00:00
Type of Address Resolution Protocol assigned.

  Last input 00:00:00, output 00:00:03, output hang never

Number of hours, minutes, and seconds since the last packet was successfully received by an interface, it is Useful for knowing when an interface failed.

Number of hours, minutes, and seconds since the last packet was successfully transmitted by an interface

Number of hours, minutes, and seconds since the interface was last reset because of a transmission that took too long. 

When the number of hours in any of the "last" fields exceeds 24 hours, the number of days and hours is printed. If that field overflows, asterisks are printed.

Last clearing of "show interface" counters never

Time at which the counters that measure cumulative statistics like number of bytes transmitted and received 
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

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 or saturation.

  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
5 minute input rate 14000 bits/sec, 15 packets/sec
5 minute output rate 4000 bits/sec, 4 packets/sec

Mentions Hardware Queue which is First in First out everytime  
Average number of bits and packets transmitted per second in the last 5 minutes.
you can even guess the transmit speed of the interface as well from the 5 minutes output , if you dont have acces to NMS

71618919 packets input, 21731123446 bytes, 0 no buffer

Total number of error-free packets received by the system 

Number of received packets discarded because there was no buffer space in the main system

Received 57218887 broadcasts (26378769 multicasts)
Total number of broadcast or multicast packets received by the interface.

0 runts, 0 giants, 0 throttles

This is quiet important this tells us Runts are the number of packets that are discarded because they are smaller than the medium's minimum packet size. i.e any Ethernet packet that is less than 64 bytes is considered a runt.

Number of packets that are discarded because they exceed the medium's maximum packet size. For example, any Ethernet packet that is greater than 1,518 bytes is considered a giant

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

Cyclic redundancy checksum generated by the originating LAN station or far-end device does not match the checksum calculated from the data received. 

On a LAN, this usually indicates noise or transmission problems on the LAN interface or the LAN bus itself. A high number of CRCs is usually the result of collisions or a station transmitting bad data or Bad data cabling or any EMI.
Number of times the 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.#

Number of received packets ignored by the interface because the interface hardware ran low on internal buffers. These buffers are different than the system buffers mentioned previously in the buffer description. Broadcast storms and bursts of noise can cause the ignored count to be increased.

0 watchdog, 26378769 multicast, 0 pause input
0 input packets with dribble condition detected

Dribble bit error indicates that a frame is slightly too long however router accepts this frame

9667499 packets output, 1711527019 bytes, 0 underruns

Number of times that the transmitter has been running faster than the router can handle. This may never be reported on some interfaces.

0 output errors, 0 collisions, 1 interface resets

Sum of all errors that prevented the final transmission of datagrams out of the interface being examined. 

Number of messages transmitted due to an Ethernet collision. This is usually the result of an overextended LAN 

A packet that collides is counted only once in output packets.

0 babbles, 0 late collision, 0 deferred

The transmit jabber timer expired.

Number of late collisions. Late collision happens when a collision occurs after transmitting the preamble.

Deferred indicates that the chip had to defer while ready to transmit a frame because the carrier was asserted.

0 lost carrier, 0 no carrier, 0 PAUSE output

Number of times the carrier was lost during transmission.
Number of times the carrier was not present during the transmission.

 0 output buffer failures, 0 output buffers swapped out

Number of failed buffers and number of buffers swapped out. 

Source :-