Packets can sometimes be dropped because of buffer overrun within the network caused by
end devices taking longer to respond than expected.
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:
-
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
-
Enter the show qos flowcontrol interface
command to check for pause frames.
-
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
-
(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.
