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Knowledge Base

FAQ - Reasons for Uneven Traffic on Eth-Trunk Member Interfaces and Solution

Publication Date:  2013-09-25  |   Views:  253  |   Downloads:  0  |   Author:  00126563  |   Document ID:  ETC0001084791


Issue Description

Why may traffic be unevenly distributed over Eth-trunk member interfaces? How to resolve the problem?


The hash algorithm determines traffic over Eth-trunk interfaces based on IP addresses, MAC addresses, or labels in packets. Traffic with the same hash elements is distributed on the same interface. If most traffic on an Eth-trunk has the same elements, traffic may be unevenly shared by interfaces in the Eth-trunk. It should be noted that hash algorithms on different devices are different, resulting in different load-sharing. Because the hash algorithm implementation is fixed, load sharing depends on hash elements, such as the MAC address, and IP address. If a device supports changing of the hash mode, you may change the hash mode. For example, you may change the MAC address-based hash mode to the IP address-based hash mode. If a device does not support changing of the hash mode, you may modify the packet encapsulation contents, for example, change the label allocation mode from label per VPN to label per route to increase the label dispersion. If the problem still persists, contact R&D to check whether hardware can be changed to resolve the problem. Note that none of the preceding methods can implement absolute even traffic distribution. Slight traffic difference over interfaces is allowed.

CX600, NE40E, and NE5000 support packet-by-packet load sharing without ensuring the packet sequence. S9300 supports hash algorithms based on the source IP address, destination IP address, source MAC address, destination MAC address, source IP address + destination IP address, source MAC address + destination MAC address, and enhanced mode.

To change the hash algorithm for Eth-trunk on CX600, NE40E, or NE5000, run the following commands:

interface eth-trunk   trunk-id

load-balance  {  mac  |  packet-all  |  ip  }

To change the hash algorithm for Eth-trunk on S9300, run the following commands:

interface eth-trunk trunk-id

load-balance { dst-ip | dst-mac | src-ip | src-mac | src-dst-ip | src-dst-mac | enhanced profile profile-name}