port-channel of 4 interfaces with no output rate...only input rate

[afsharki2]

Hello, I have a bunch of port-channels that have 4 interfaces linked to them.

Why is it that only 2 of interfaces show a "30 second output rate 0 bits/sec, 0 packets/sec" under "show interface" and have normal input rates.

is this something with the port-channel configurations that makes 2 of the interface not output traffic.

These are the 4 interfaces in the pagp port-channel:

Switch1#sh int t1/1/6   
  30 second input rate 317000 bits/sec, 169 packets/sec
  30 second output rate 38090000 bits/sec, 5616 packets/sec

          
Switch1#sh int t1/1/5
  30 second input rate 1846000 bits/sec, 880 packets/sec
  30 second output rate 25927000 bits/sec, 4325 packets/sec

          
Switch1#sh int t2/1/5
  30 second input rate 515000 bits/sec, 237 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec

          
Switch1#sh int t2/1/6
  30 second input rate 14208000 bits/sec, 2423 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec

These are the counters:
 

Switch1#sh int t2/1/5 counter

Port                  InBytes   InUcastPkts   InMcastPkts   InBcastPkts
Te2/1/5         9887096678034   37586027362      12091339      48982047

Port                 OutBytes  OutUcastPkts  OutMcastPkts  OutBcastPkts
Te2/1/5        11429315477991   12179268874       3550021       1114871
Switch1#sh int t2/1/6 counter

Port                  InBytes   InUcastPkts   InMcastPkts   InBcastPkts
Te2/1/6        16307118524351   50713982712      15148528      63558571

Port                 OutBytes  OutUcastPkts  OutMcastPkts  OutBcastPkts
Te2/1/6         4156839382844    5679773089       5987049       7680701
Switch1#sh int t1/1/6 counter

Port                  InBytes   InUcastPkts   InMcastPkts   InBcastPkts
Te1/1/6        10034774352417   39653084589      18145803      38882592

Port                 OutBytes  OutUcastPkts  OutMcastPkts  OutBcastPkts
Te1/1/6        189372703971619  174906765970       3266534       6687054
Switch1#sh int t1/1/5 counter

Port                  InBytes   InUcastPkts   InMcastPkts   InBcastPkts
Te1/1/5        13966434357936   49859031974      33541931      73303464

Port                 OutBytes  OutUcastPkts  OutMcastPkts  OutBcastPkts
Te1/1/5        196915105905576  176988906709     221324366      47603699

Thanks in advance and let me know if you need more info

[Madhukrishnan Gopinathan Nair]

It could be due to port-channel load balancing. Please note that the when you add more than 1 interface to a port-channel, it does not mean you are going to load balance the traffic. Every time  a traffic flow comes to the switch needing to go out of Port-channel, it calculate the hash and then selects one of the link, so for example if you have 2 ports in one PO, and have only 1 flow passing through, effectively it will use only 1 link.

Hope this helps,

Madhu

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[Steve Fuller · Accepted solution]

Hi,

I'd agree with Madhu that it looks as if the load balancing is not that efficient.

And to add to what he's already included, you can determine the current port-channel load balancing mechanism using the show etherchannel load-balance command, and can change it using the port-channel load-balance <mode> command in global configuration.

To achieve good load balancing you ideally want to use source and destination addresses, and include MAC, IP and TCP/UDP port if supported by the platform.

Note also that the balancing used by one partner is totally independent of the balancing of the other partner. To ensure you achieve good balancing in both directions you would need to check both switches.

Regards