CCIE Pursuit Blog

August 11, 2007

show interface [interface] counters etherchannel

Filed under: Cisco,Cisco Certification,Cool Commands,Switching,Tech Tips — cciepursuit @ 3:09 pm

I was mucking with etherchannel today and discovered a cool command that I was not aware of: show interface [interface] counters etherchannel.

You can run this command on your port-channel interface:

sw4#sh int po1 count ether

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1                23863            15           229             0
Fa0/19           1899894           835         18864             0
Fa0/20           1903864           835         18862             5
Fa0/21           1945733           835         19307             5

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1                 3653            15            14             0
Fa0/19            181124           834           533             5
Fa0/20            171050           834           494             0
Fa0/21            169510           834           469             0

If you run it on one of the bundled links, you’ll get an error message:

sw4#sh int fa0/19 count ether
Etherchannel not enabled on this interface

Clearing the counters for this command takes  a bit of work.  If you clear the counters on the port-channel interface, it will not clear the counters on the individual bundled links:

sw4#clear count po1
Clear “show interface” counters on this interface [confirm]
sw4#
*Mar  1 02:20:57: %CLEAR-5-COUNTERS: Clear counter on interface Port-channel1 by console
sw4#sh int po1 count eth

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1                 1504             3            13             0 <-cleared
Fa0/19           1900270           838         18865             0
Fa0/20           1904240           838         18863             5
Fa0/21           1959175           838         19447             5

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1                    0             0             0             0 <-cleared
Fa0/19            181500           837           534             5
Fa0/20            171426           837           495             0
Fa0/21            169886           837           470             0

You can clear each bundled link on its own:

sw4#clear count fa0/19
*Mar  1 02:25:35: %CLEAR-5-COUNTERS: Clear counter on interface FastEthernet0/19 by console
sw4#sh int po1 count eth

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1               136047            87          1311             0
Fa0/19                94             1             0             0 <-cleared
Fa0/20           1909733           866         18877             5
Fa0/21           2082732           866         20717             5

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1                16479            84            42             0
Fa0/19                 0             0             0             0 <-cleared
Fa0/20            176919           865           509             0
Fa0/21            175379           865           484             0

You can clear both the port-channel and the bundled links’ counters all at once with “clear counters”.  Personally, I very rarely use that command.  I feel that it’s like dropping a nuke on a mosquito.  Sure you clear the counters that you want cleared, but you also destroy a ton of historical data by wiping out the all of the counters.  I hate trying to troubleshoot an issue after another engineer has run this command.  But if you must use it 🙂

sw4#clear count
Clear “show interface” counters on all interfaces [confirm]
*Mar  1 03:40:48: %CLEAR-5-COUNTERS: Clear counter on all interfaces by console
sw4#sh int po1 count eth

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1                 1222             0            13             0
Fa0/19                 0             0             0             0
Fa0/20                 0             0             0             0
Fa0/21              1222             0            13             0

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1                    0             0             0             0
Fa0/19                 0             0             0             0
Fa0/20                94             1             0             0
Fa0/21                94             1             0             0

You can use this command to illustrate the method that the switch is using to “load balance” over the etherchannel links:

First, let’s create an SVI on each side of the Etherchannel
sw4(config)#vlan 100
sw4(config-vlan)#int vlan 100
sw4(config-if)#ip address 100.0.0.4 255.255.255.0

sw3(config)#vlan 100
sw3(config-vlan)#int vlan 100
sw3(config-if)#ip address 100.0.0.3 255.255.255.0

Let’s clear etherchannel counters, then ping the hell out of the 100.0.0.3 address:
sw4#sh int po1 count eth

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1                 3760             0            40             0
Fa0/19               188             2             0             0
Fa0/20                94             1             0             0
Fa0/21              5828             1            61             0

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1                  282             3             0             0
Fa0/19               188             2             0             0
Fa0/20               188             2             0             0
Fa0/21                94             1             0             0

sw4#ping 100.0.0.3 re 10000 si 1500
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
—–output truncated—–
Success rate is 100 percent (10000/10000), round-trip min/avg/max = 1/2/28 ms

Now let’s look at the etherchannel counters:
sw4#sh int po1 count eth

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po1             15512981         10018           323             0
Fa0/19          15481343         10008             3             0 <-note
Fa0/20              1249             7             3             0
Fa0/21             32739             7           338             0

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po1             15483747         10021             9             0
Fa0/19          15481343         10008             3             0 <-note
Fa0/20              1343             8             3             0
Fa0/21              1249             7             3             0

So why did one interface handle all of the pings?  Let’s use another nifty little command to find out:

sw4#show etherchannel load-balance
EtherChannel Load-Balancing Operational State (src-mac):
Non-IP: Source MAC address
  IPv4: Source MAC address
  IPv6: Source IP address

sw4#sh arp | i 100.0.0.4
Internet  100.0.0.4               –   000a.8a1c.c400  ARPA   Vlan100

We are “load balancing” based on the source mac-address.  The ping is sourced by 100.0.0.4 and the source-mac address will not change, so all of our pings took the same route.  This is good to know for the real world as well.  Depending on the traffic source, that 8-gig etherchannel you set up to the server may only be giving you 1 gig of possible bandwidth.  🙂


Cisco Documentation:

show interfaces counters

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