[All About Switches] Packets Are Unevenly Load Balanced Among Eth-Trunk Member Interfaces That Transmit Multicast Packets

Created: Mar 9, 2018 10:21:54Latest reply: Mar 9, 2018 12:42:48 1004 1 0 0

Involved Products and Versions

All products and versions

Networking

None

Fault Symptom

Packets are unevenly load balanced among Eth-Trunk7 member interfaces on a switch. (Packet transmission on GE3/0/9 is faulty, which can be ignored in this case, You only need to pay attention to the other member interfaces.)

<Switch> 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-Trunk7                  up    up       5.95%    62%          0          0
 GigabitEthernet3/0/7       up    up       5.79%   100%          0          0
 GigabitEthernet3/0/8       up    up       5.93%    51%          0          0
 GigabitEthernet3/0/9       up    up       0%        0%          0          0
 GigabitEthernet4/0/23      up    up       4.53%     60%         0          0
 GigabitEthernet4/0/24      up    up       7.55%     39%         0          0

Cause Analysis

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 is used for non-unicast packets. Since the load-balance command is used for Eth-Trunk7 while multicast packets are transmitted on member interfaces of Eth-Trunk7, packets are unevenly load balanced.

Troubleshooting Procedure

                          Step 1     Check the configuration of Eth-Trunk7 and find that enhanced load balancing is configured on the switch.

[Switch-Eth-Trunk7] display this
#
interface Eth-Trunk7
undo port hybrid vlan 1
port hybrid tagged vlan 5 44 83 901 to 904 931 999 2041 to 2048 2215 to 2227 2229 2250
port vlan-stacking vlan 341 to 388 stack-vlan 590
mode lacp-static
load-balance enhanced profile 1
#

[Switch-load-balance-profile-1] display this
#
load-balance-profile 1
l2 field smac dmac l2-protocol vlan sport dport
ipv4 field sip dip vlan l4-sport l4-dport protocol sport dport

                          Step 2     Run the display interface command to view interfaces where packets are unevenly load balanced and find that most of outbound packets are multicast packets.

Check interfaces of the live network, and find that the inbound bandwidth usage of GE3/0/44 on the switch is 100% and transmitted packets are almost multicast packets.

<Switch> display interface gigabitethernet 3/0/44
GigabitEthernet3/0/44 current state : UP
Line protocol current state : UP
Description:To QuanQiuYan_DSLAM_ZhuanXian
Switch Port, PVID : 1, TPID : 8100(Hex), The Maximum Frame Length is 9216
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is e468-a3a2-0ae0
Last physical up time : 2017-11-10 15:40
Last physical down time : 2017-11-10 15:40
Current system time: 2017-11-10 15:40
Port Mode: COMMON COPPER
Speed : 1000, Loopback: NONE
Duplex: FULL, Negotiation: ENABLE
Mdi : AUTO
Last 300 seconds input rate 1000018440 bits/sec, 1097253 packets/sec
Last 300 seconds output rate 2408 bits/sec, 3 packets/sec
Input peak rate 1000000000 bits/sec, Record time: 2017-11-10 15:40
Output peak rate 999999864 bits/sec, Record time: 2017-11-10 15:40
 
Input: 105965324838 packets, 12066603804412 bytes
Unicast: 0, Multicast: 105953299654
Broadcast: 12025160, Jumbo: 0
Discard: 0, Total Error: 0
 
CRC: 0, Giants: 0
Jabbers: 0, Fragments: 0
Runts: 0, DropEvents: 0
Alignments: 0, Symbols: 0
Ignoreds: 0, Frames: 0
 
Output: 346132 packets, 30459616 bytes
Unicast: 0, Multicast: 0
Broadcast: 346132, Jumbo: 0
Discard: 0, Total Error: 0
 
Collisions: 0, ExcessiveCollisions: 0
Late Collisions: 0, Deferreds: 0
Buffers Purged: 0
 
Input bandwidth utilization threshold : 100.00%
Output bandwidth utilization threshold: 100.00%
Input bandwidth utilization : 100%
Output bandwidth utilization : 0%

                          Step 3     Capture packets on GigabitEthernet3/0/44 and find that multicast packets on this interface are from VLAN 999.

[Switch] capture-packet interface gigabitethernet 3/0/44 destination terminal packet-num 10
Info: Captured packets will be shown on terminal. 
[Switch]
Packet: 1
-------------------------------------------------------
33 33 00 00 00 01 4c 11 bf 01 d5 2a 81 00 03 e7 
86 dd 60 00 00 00 00 20 3a ff 20 01 0d a8 02 07 
00 00 00 00 00 00 00 00 94 02 ff 02 00 00 00 00 
00 00 00 00 00 00 00 00 00 01 88 00 ee fc 20 00 
-------------------------------------------------------
 
Packet: 2
-------------------------------------------------------
33 33 ff 00 94 02 4c 11 bf 01 d5 2a 81 00 03 e7 
86 dd 60 00 00 00 00 18 3a ff 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 ff 02 00 00 00 00 
00 00 00 00 00 01 ff 00 94 02 87 00 22 f3 00 00 
-------------------------------------------------------

                          Step 4     Run the multicast drop-unknown in the VLAN 999 to configure the switch to discard unknown multicast packets. After the interface traffic is normal, packets are evenly load balanced among Eth-Trunk7 member interfaces.

----End

  • x
  • convention:

ahricomambo4u  Visitor   Created Mar 9, 2018 12:42:48 Helpful(0) Helpful(0)

Hi,
How about multicast packets between switches iStacked together. Will it have the same issue? Will the multicast packets be distributed between the iStacked ports?
  • x
  • convention:

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