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Knowledge Base

Load Unbalancing Occurs When an IP-Trunk Performs the Hash Algorithm Based on the Source and Destination IP Addresses

Publication Date:  2019-07-09  |   Views:  1260  |   Downloads:  0  |   Document ID:  EKB1000038556


Issue Description

On the customer's live network, an NE40 router of version 5.30 (NE40&80 V300R002C01B599) provides Internet Protocol television (IPTV) live broadcast service. Two POS interfaces (6/0/0 and 6/0/1) on the NE40 router are bundled into an IP-Trunk to send packets to a multicast group (containing multiple multicast sources). The load-balance src-dst-ip command is executed to configure IP-Trunk load balancing, but the two POS interfaces fail to balance traffic (traffic proportion reaching 2:1).

Alarm Information

eSight is used as the network management platform. Based on statistics collected by eSight software, bandwidth usage of POS6/0/0 reaches 80% for a long period of time, while that of POS6/0/1 only reaches about 40%. eSight prompts an orange alarm.

Handling Process

The direct solution is to change the IP addresses. IP addresses on the customer's live network are fixed and cannot be modified. Therefore, replace the load-balance src-dst-ip command with the load-balance packet-all command that performs the hash algorithm on all packets. In this way, load balancing is implemented.

Root Cause

The load-balance src-dst-ip command is executed to configure IP-Trunk load balancing. However, this command configures an IP-Trunk to perform the hash algorithm based on the source and destination IP addresses. The last bits of the source and destination IP addresses are used to perform exclusive OR (XOR) operation. The operation result (0 or 1) is used as the basis for traffic allocation. Collect relevant configurations. It is found that the IP-Trunk address is XXX.XXX.0.117 30 and multicast network segments in the multicast group are as follows:
XXX.XXX.41.0 24
XXX.XXX.43.64 26
XXX.XXX.43.32 27
XXX.XXX.43.16 28
XXX.XXX.43.8 32
XXX.XXX.43.128 25
XXX.XXX.145.0 24
XXX.XXX.43.10 32
XXX.XXX.43.11 32
XXX.XXX.43.13 32
XXX.XXX.43.12 32
XXX.XXX.43.14 32
XXX.XXX.43.15 32
XXX.XXX.45.192 26
XXX.XXX.45.132 32
XXX.XXX.45.150 32
XXX.XXX.45.12 32
XXX.XXX.45.11 32    
XXX.XXX.45.18 32
The XOR operation is performed. Fifteen 1s and three 0s are found in the XOR operation result. The proportion of operation result 1 to operation result 0 is 5:1. Such an algorithm results in unbalanced traffic on the interfaces, failing to reach the expected load balancing effect.


IP addresses should be well planned and assigned for load balancing.