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S12700 V200R012C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Configuring a MAC Hash Algorithm

Configuring a MAC Hash Algorithm


Generally, it is recommended to use the default MAC hash algorithm unless you have specific requirements.

The switch typically uses a hash algorithm to learn MAC address entries. However, conflicts may occur if two or more MAC addresses produce the same hash value. In this case, the switch may fail to learn many MAC addresses and then will broadcast traffic destined for these MAC addresses. The heavy broadcast traffic increases the load on the switch. To mitigate this issue, use an appropriate hash algorithm to mitigate the hash conflict.

  • MAC addresses of LPUs are stored using the following modes:

    • Hash bucket

      The LPU that uses the hash bucket performs hash calculation for VLAN IDs and MAC addresses in MAC address entries to be stored and obtains hash bucket indexes. The MAC addresses with the same hash bucket index are stored in the same hash bucket. If a hash bucket with the maximum storage space cannot accommodate learned MAC addresses of the hash bucket, a hash conflict occurs and MAC addresses cannot be stored. The maximum number of MAC addresses learned by an LPU through the hash bucket may be not reached.

    • TCAM chip

      The LPU that uses the TCAM mode stores all learned MAC addresses in the TCAM chip in sequence. As long as the number of learned MAC addresses does not reach the maximum value, MAC addresses can be learned. In TCAM mode, the switch must be equipped with the enhanced LPU that uses the TCAM chip.

    SA series, EA series, SC series, X series, and EE series cards and ET1D2X48SEC0 cards use the hash bucket, so the maximum number of MAC addresses learned by these cards may be not reached. Other LPUs excluding SA series, EA series, SC series, X series, EE series card and ET1D2X48SEC0 cards use the TCAM mode by default.

  • X series cards do not support this function.
  • MAC addresses are distributed on a network randomly, so the best hash algorithm cannot be determined. Generally, it is recommended to use the default MAC hash algorithm unless you have specific requirements.

  • An appropriate hash algorithm can reduce hash conflicts, but cannot prevent them.

  • After the hash algorithm is changed, restart the card to make the configuration take effect.


  1. Run system-view

    The system view is displayed.

  2. Run mac-address hash-mode { crc16-lower | crc16-upper | crc32-lower | crc32-upper | lsb } slot slot-id

    A hash algorithm is configured on the specified LPU.

    The default hash algorithm is crc32-lower.

Verifying the Configuration

Run the display mac-address hash-mode command to check the running and configured hash algorithms.

Updated: 2019-01-18

Document ID: EDOC1100038103

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