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Knowledge Base

Load Imbalance Occurs When Load Balancing Based on Source and Destination IP Addresses Is Performed on an IP-Trunk Interface

Publication Date:  2019-07-09  |   Views:  493  |   Downloads:  0  |   Document ID:  EKB1001909051

Contents

Issue Description

An NE40E&80E running Version 5.30 (NE40&80 V300R002C01B599) is deployed on the customer's live network for live IPTV services. Two POS interfaces (6/0/0 and 6/0/1) are bound as an IP-Trunk interface on the NE40E&80E to send packets to a multicast group (including multiple multicast sources). After a load-balancing mode is configured for the IP-Trunk interface using the load-balance src-dst-ip command, load imbalance occurs with a big difference (2:1) in traffic on the two POS interfaces.

Alarm Information

eSight is used as the management platform. According to the statistics of the NMS software, the bandwidth usage of the POS interface 6/0/0 remains 80% for a long time, where that of the POS interface 6/0/1 is around 40%. The NMS displays an orange warning.

Handling Process

The most direct way to solve this problem is to modify the allocated addresses. In this example, the addresses on the customer's live network are fixed and cannot be adjusted. Therefore, the load-balance src-dst-ip command is replaced by the load-balance packet-all command which performs load balancing based on all packets.

Root Cause

The customer configures a load balancing mode for the IP-Trunk interface using the load-balance src-dst-ip command. The command enables the device to hash packets based on source and destination IP addresses. The hash algorithm uses the last bit (binary) of the source and destination IP addresses to perform the Exclusive-OR calculation. In this way, the system distributes traffic based on the result (0 or 1). After related configuration data is collected, the IP-Trunk address of the user is 182.x.x.117 30. The addresses of the multicast network segments in the multicast group are as follows:

238.x.x.0 24
238.x.x.64 26
238.x.x.32 27
238.x.x.16 28
238.x.x.8 32
238.x.x.128 25
238.x.x.0 24
238.x.x.10 32
238.x.x.11 32
238.x.x.13 32
238.x.x.12 32
238.x.x.14 32
238.x.x.15 32
238.x.x.192 26
238.x.x.132 32
238.x.x.150 32
238.x.x.12 32
238.x.x.11 32    
238.x.x.18 32

Based on the preceding analysis, after the Exclusive-OR calculation is perform, the number of 1 is 15, and the number of 0 is 3. The proportion is 5:1. If this algorithm is used, load imbalance will occur, and the expected load balancing cannot be achieved.

Suggestions

If load balancing needs to be considered during IP address planning, plan IP addresses properly to achieve better load balancing.