[All About Switches] Packets Are Unevenly Load Balanced Among Eth-Trunk Interfaces After Unicast Packets Are Converted into Broadcast Packets

Latest reply: Mar 9, 2018 05:52:37 1189 1 0 0

Involved Products and Versions

All products and versions

Networking

None

Fault Symptom

Packets are unevenly load balanced among Eth-Trunk20 member interfaces on a switch.

<Quidway> display interface brief
PHY: Physical
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
(b): BFD down
(d): Dampening Suppressed
InUti/OutUti: input utility/output utility
Interface                   PHY   Protocol InUti OutUti   inErrors  outErrors
Eth-Trunk20                 up    --       0.38%    25%          0          0
  GigabitEthernet3/0/18     up    --       0.02%     1%          0          0
  GigabitEthernet3/0/19     up    --       0.74%  0.04%          0          0
  GigabitEthernet3/0/20     up    --       0.62%    98%          0          0
  GigabitEthernet3/0/21     up    --       0.14%     1%          0          0

Cause Analysis

The switch keeps receiving TC packets from its connected devices, and unicast packets are converted into broadcast packets, resulting in uneven load balancing among Eth-Trunk member interfaces.

Troubleshooting Procedure

                          Step 1     According to the interface traffic of the switch on the live network, attempt to adjust hash factors to solve the uneven load balancing among Eth-Trunk20 member interfaces. This problem persists after several attempts. The customer reported that this problem occurred after an operation was performed at around 14:20.

                          Step 2     Check switch logs and find that a large number of TC packets were generated since 14:20 and the switch kept deleting MAC addresses.

Oct 31 2017 14:20:57 Quidway %MSTP/6/RECEIVE_MSTITC(l): MSTP received BPDU with TC, MSTP process 0 instance 0, port name is GigabitEthernet8/0/0.
Oct 31 2017 14:20:59 Quidway %MSTP/6/RECEIVE_MSTITC(l): MSTP received BPDU with TC, MSTP process 0 instance 0, port name is GigabitEthernet8/0/0.
Oct 31 2017 14:20:59 Quidway %MSTP/6/RECEIVE_MSTITC(l): MSTP received BPDU with TC, MSTP process 0 instance 0, port name is GigabitEthernet8/0/34.

[Quidway-hidecmd] display stp tc 
 ---------- Stp Instance 0 tc or tcn count ----------
 Port GigabitEthernet6/0/0    0
 Port Ethernet12/0/0          1079
 Port Ethernet12/0/1          0
 Port Ethernet12/0/3          0
......
 Port GigabitEthernet7/0/1    0
 Port GigabitEthernet8/0/0    9357
 Port GigabitEthernet8/0/2    0
 Port GigabitEthernet8/0/6    0           
 Port GigabitEthernet8/0/34   14
 Port GigabitEthernet8/0/35   0
......
 Port Eth-Trunk18             0
 Port Eth-Trunk20             0
 Port Eth-Trunk100            0
 Port Eth-Trunk21             0
 Port Eth-Trunk22             0
 Port Eth-Trunk23             0
 ---------- Stp Instance 10 tc or tcn count ----------

                          Step 3     Run the display mac-address summary command and view diagnosis logs, and find that the switch keeps deleting and relearning MAC addresses.

<Quidway> display mac-address summary
----------------------------------------------------------------              
Slot  Total    Blackhole  Static  Dynamic  DLocal    DRemote   
----------------------------------------------------------------           
   1   1820            0       0     1820      1680       140
   2   3116            0       0     3116      1833      1283
   3    374            0       0      374       333        41
   4     77            0       0       77        49        28
   5    162            0       0      162       134        28
   6   1415            0       0     1415        49      1366
   7   9324            0       0     9324      9131       193
   8   1238            0       0     1238      1165        73
   9    712            0       0      712       629        83
  10   1866            0       0     1866      1738       128
  11    393            0       0      393       389         4
  12     21            0       0       21        10        11
----------------------------------------------------------------             

<Quidway> display mac-address summary
----------------------------------------------------------------              
Slot  Total    Blackhole  Static  Dynamic  DLocal    DRemote   
----------------------------------------------------------------           
   1    890            0       0      890       750       140
   2   2667            0       0     2667      1384      1283
   3    670            0       0      670       629        41
   4     81            0       0       81        53        28
   5    176            0       0      176       148        28
   6   1414            0       0     1414        48      1366
   7   9327            0       0     9327      9134       193
   8   1420            0       0     1420      1347        73
   9    909            0       0      909       826        83
  10   1362            0       0     1362      1234       128
  11    439            0       0      439       435         4
  12     22            0       0       22        11        11
----------------------------------------------------------------

Oct 31 2017 14:20:57 Quidway %MSTP/5/TCM_DEL_MACARP(D): MSTP enters TCM, notifies L2IF to delete all MAC entries and ARP entries of instance 0.

                          Step 4     The switch differentiates unicast and non-unicast packets during load balancing among Eth-Trunk member interfaces, and different commands are configured for these packets. The load-balance command is used for unicast packets, and the unknown-unicast load-balance command (which is not supported in V100R002) is used for non-unicast packets.

After the switch receives TC packets, network convergence is triggered because of network topology changes. During the convergence, the switch deletes and relearns MAC addresses and ARP entries to ensure that packets are forwarded normally.

However, the switch keeps deleting MAC addresses because TC packets are constantly sent to GigabitEthernet8/0/0, and therefore unicast packets are converted into broadcast packets. As a result, packets are unevenly load balanced among Eth-Trunk member interfaces. This is why the method of adjusting hash factors does not take effect.

Run the stp edged-port enable command on GigabitEthernet8/0/0. TC packets do not increase on the switch and packets are evenly load balanced among Eth-Trunk20 member interfaces.

<Quidway> display interface brief
PHY: Physical
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
(b): BFD down
(d): Dampening Suppressed
InUti/OutUti: input utility/output utility
Interface                   PHY   Protocol InUti OutUti   inErrors  outErrors
Eth-Trunk20                 up    --       0.30%    25%          0          0
  GigabitEthernet3/0/18     up    --       0.01%    20%          0          0
  GigabitEthernet3/0/19     up    --       0.61%    17%          0          0
  GigabitEthernet3/0/20     up    --       0.50%    46%          0          0
  GigabitEthernet3/0/21     up    --       0.10%    17%          0          0

----End

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doctor.zhang
Created Mar 9, 2018 05:52:37 Helpful(0) Helpful(0)

[All About Switches] Packets Are Unevenly Load Balanced Among Eth-Trunk Interfaces After Unicast Packets Are Converted into Broadcast Packets-2632143-1good
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