[c-nsp] OutDiscards

[Dmitry Kiselev]

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!

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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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-- 
Dmitry Kiselev