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[EX] Mac-limit value for VLAN

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Article ID: KB26462 KB Last Updated: 05 Mar 2017Version: 2.0
Summary:
This article describes the issue of the switch not learning MAC addresses, other than the automatic MAC addresses, when mac-limit is set to 1.
Symptoms:
  • MAC limiting protects against flooding of the Ethernet switching table on the EX Series switch.

  • MAC limiting sets a limit on the number of MAC addresses that can be learned.
Cause:
Junos allows the configuration of mac-limit on a VLAN. Based on the following default behavior, pay attention to setting mac-limit as 1:

When a RVI (Routed VLAN Interfaces) is assigned for the VLAN, the first MAC address that is inserted into the forwarding database is the MAC address of the RVI. If any LAG (Aggregated Ethernet bundles) js using LACP, the first MAC address that is inserted into the forwarding database is the source address of the protocol packet.

So, the switch will not learn the MAC addresses, other than the automatic addresses, when mac-limit is set to 1.
Solution:
If a RVI (Routed VLAN Interfaces) or LAG (Aggregated Ethernet bundles) interface that uses using LACP is already present in a VLAN, the mac-limit should be set to at least 2. Otherwise, MAC addresses will not be learnt on the VLAN, as expected.

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