Verifying packets dropped because of high-latency end device

For example, an overloaded disk array can cause such latency, as can a host that does not process data as quickly as expected. Devices that stop receiving data for an extended period of time can cause excessive latency.

The ultimate solution to these problems is to fix the end device itself. However, some adjustments to the device and network configuration can help to reduce the problem.

To detect and relieve congestion and dropped packets resulting from latency in end devices, perform the following steps:

  1. Enter the show lldp neighbors detail command to check under "DCBX TLVs" that the end device is DCB-ready and confirm that the end device is also advertising its DCB capabilities. 
    device# show lldp neighbors detail 
Neighbors for Interface Eth 0/11 

MANDATORY TLVs 
===============
Local Interface: Eth 0/11  (Local Interface MAC: 609c.9fde.2621)
Remote Interface: Ethernet 0/1 (Remote Interface MAC: d884.66ea.4b17)
Dead Interval: 120 secs    
Remaining Life : 91 secs
Chassis ID: d884.66ea.4b14
LLDP PDU Transmitted: 2153  Received: 2153

OPTIONAL TLVs 
==============
Port Interface Description: Eth 0/1
System Name: R60-SN

DCBX TLVs 
===========
Version : CEE 
DCBX Ctrl OperVersion: 0  MaxVersion: 0  SeqNo: 2 AckNo: 2
DCBX ETS OperVersion: 0  MaxVersion: 0  Enabled: 1  Willing: 0 Error: 0
Enhanced Transmission Selection (ETS) 
  Priority-Group ID Map:
    Priority : 0  1  2  3  4  5  6  7
    Group ID : 0  0  0  0  0  0  0  0 
  Group ID Bandwidth Map:
    Group ID  :   0   1   2   3   4   5   6   7 
    Percentage:   0   0   0   0   0   0   0   0 
    Number of Traffic Classes supported: 8
DCBX PFC OperVersion: 0  MaxVersion: 0  Enabled: 1  Willing: 0 Error: 0
Priority-based Flow Control (PFC)
     Enabled Priorities: none
     Number of Traffic Class PFC supported: 8
LAN LLS OperVersion: 0  MaxVersion: 0  Enabled: 1  Willing: 0 Error: 0
LAN  Logic Link Status: Up
  2. Enter the show qos flowcontrol interface command to check for pause frames.
  3. Enter the show qos interface command to check the QoS configuration. 
    SLX# show qos interface ethernet 0/2 
[Note: CoS = Class of Service, TC = Traffic Class, DP = Drop Precedence]
Interface Ethernet 0/2
  Provisioning Mode: none
  Default TC: 0

  CoS-to-TC Map: default
             In-CoS: 0  1  2  3  4  5  6  7
      -------------------------------------
             Out-TC: 0  1  2  3  4  5  6  7
             Out-DP: 0  0  0  0  0  0  0  0

  TC-to-CoS Map: default
              In-TC: 0  1  2  3  4  5  6  7
      -------------------------------------
      Out-CoS(DP=0): 0  1  2  3  4  5  6  7
      Out-CoS(DP=1): 0  1  2  3  4  5  6  7
      Out-CoS(DP=2): 0  1  2  3  4  5  6  7
      Out-CoS(DP=3): 0  1  2  3  4  5  6  7

  DSCP Mutation Map: default (DSCP = d1d2)
      d1 :  d2 0  1  2  3  4  5  6  7  8  9
      -------------------------------------
       0 :    00 01 02 03 04 05 06 07 08 09
       1 :    10 11 12 13 14 15 16 17 18 19
       2 :    20 21 22 23 24 25 26 27 28 29
       3 :    30 31 32 33 34 35 36 37 38 39
       4 :    40 41 42 43 44 45 46 47 48 49
       5 :    50 51 52 53 54 55 56 57 58 59
       6 :    60 61 62 63

  DSCP-to-TC Map: default (x/y: TC = x, DP = y, DSCP = d1d2)
      d1 :  d2  0   1   2   3   4   5   6   7   8   9 
      ------------------------------------------------
       0 :     0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 1/0 1/0
       1 :     1/0 1/0 1/0 1/0 1/0 1/0 2/0 2/0 2/0 2/0
       2 :     2/0 2/0 2/0 2/0 3/0 3/0 3/0 3/0 3/0 3/0
       3 :     3/0 3/0 4/0 4/0 4/0 4/0 4/0 4/0 4/0 4/0
       4 :     5/0 5/0 5/0 5/0 5/0 5/0 5/0 5/0 6/0 6/0
       5 :     6/0 6/0 6/0 6/0 6/0 6/0 7/0 7/0 7/0 7/0
       6 :     7/0 7/0 7/0 7/0

  DSCP-to-CoS Map: default (DSCP = d1d2)
      d1 :  d2 0  1  2  3  4  5  6  7  8  9
      -------------------------------------
       0 :    00 00 00 00 00 00 00 00 01 01
       1 :    01 01 01 01 01 01 02 02 02 02
       2 :    02 02 02 02 03 03 03 03 03 03
       3 :    03 03 04 04 04 04 04 04 04 04
       4 :    05 05 05 05 05 05 05 05 06 06
       5 :    06 06 06 06 06 06 07 07 07 07
       6 :    07 07 07 07

  Per Traffic-Class Tail Drop Threshold (bytes)
             TC:      0      1      2      3      4      5      6      7
      ------------------------------------------------------------------
      Threshold:      0      0      0      0      0      0      0      0

  Flow control mode Off

  Traffic Class Scheduler configured for 8 Strict Priority queues
  4. (If needed) Reconfigure QoS.
    For detailed information, refer to the QoS sections of the Extreme SLX-OS Layer 2 Switching Configuration Guide and the Extreme SLX-OS Layer 3 Routing Configuration Guide.
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