[c-nsp] OutDiscards

[Gabor Ivanszky]

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Hello Dmitry,

how is your output traffic distributed among physical GE interfaces?
If 2.5Gbps traffic is polarized to some certain output ports - instead
of even distribution - it could easily overload those GE ports. If
that is case, you could try different load-balancing algorithms on the
etherchannel.

You could find more information about 3750-E switching architecture at
www.lenovocast.com/files/subsystems/12073/BRKRST-1001.pdf , but in
your case this doesn't seem to be the bottleneck.

regards,
Gabor

Dmitry Kiselev wrote:
> Hello!
>
> I have a 3750E switch runing 12.2(40)SE IOS for very simple task:
> just layer2 trunk switching between TenGigabitEthernet t1/0/1-2
> ports and 8-ports GigabitEtherChannel po1. Bandwidth usage about
> 2-4Gbps. There no problems with 10G ports, but a lot of OutDiscards
> on all GEC ports and Po1 interface. According to various Cisco
> documents common cause of OutDiscards a lack of buffer space due
> interfaces speed missmatch. I already increased hold-queue to 4096
> on all GEC ports and Po1 itself, but it just reduce OutDiscards a
> bit.
>
> So, my question is: is it possible to avoid OutDiscards for traffic
>  came from 10G towards 8-ports GEC?
>
> Thanks!
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>
> interface GigabitEthernet1/0/1 switchport trunk encapsulation dot1q
>  switchport mode trunk channel-group 1 mode active hold-queue 4096
> in hold-queue 4096 out ! interface Port-channel1 description
> g1/0/1-8 GEC switchport trunk encapsulation dot1q switchport mode
> trunk hold-queue 4096 in hold-queue 4096 out ! interface
> TenGigabitEthernet1/0/1 switchport trunk encapsulation dot1q
> switchport mode trunk hold-queue 4096 in hold-queue 4096 out !
> interface TenGigabitEthernet1/0/2 switchport trunk encapsulation
> dot1q switchport mode trunk hold-queue 4096 in hold-queue 4096 out
>
>
> orion#sh etherchannel 1 sum ... Group  Port-channel  Protocol
> Ports
> ------+-------------+-----------+-----------------------------------------------
>  1      Po1(SU)         LACP      Gi1/0/1(P)  Gi1/0/2(P)
> Gi1/0/3(P) Gi1/0/4(P)  Gi1/0/5(P)  Gi1/0/6(P) Gi1/0/7(P)
> Gi1/0/8(P)
>
> orion#sh int t1/0/1 | inc bits 1 minute input rate 4115286000
> bits/sec, 487916 packets/sec 1 minute output rate 1966100000
> bits/sec, 420757 packets/sec orion#sh int t1/0/2 | inc bits 1
> minute input rate 1084695000 bits/sec, 262525 packets/sec 1 minute
> output rate 3020117000 bits/sec, 311735 packets/sec orion#sh int
> po1 | inc bits 1 minute input rate 2307647000 bits/sec, 384003
> packets/sec 1 minute output rate 2520425000 bits/sec, 402044
> packets/sec
>
>
> orion#sh int t1/0/1 count err
>
> Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err
> UnderSize  OutDiscards Te1/0/1             0           0
> 0           0          0            0
>
> Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen
> Runts     Giants Te1/0/1            0          0          0
> 0          0          0          0
>
> orion#sh int t1/0/2 count err
>
> Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err
> UnderSize  OutDiscards Te1/0/2             0           0
> 0           0          0            0
>
> Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen
> Runts     Giants Te1/0/2            0          0          0
> 0          0          0          0
>
> orion#sh int po1 count err
>
> Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err
> UnderSize  OutDiscards Po1                 0           0
> 0           0          0     31985848
>
> Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen
> Runts     Giants Po1                0          0          0
> 0          0          0          0
>
> <-about 5 sec wait->
>
> orion#sh int po1 count err
>
> Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err
> UnderSize  OutDiscards Po1                 0           0
> 0           0          0     31987480
>
> Port      Single-Col  Multi-Col   Late-Col  Excess-Col  Carri-Sen
> Runts     Giants Po1                0          0          0
> 0          0          0          0
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>

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