Limiting MAC Addresses with ESRP Enabled

If you configure a MAC address limit on VLANs that participate in an ESRP (Extreme Standby Router Protocol) domain, you should add an additional back-to-back link (that has no MAC address limit on these ports) between the ESRP-enabled switches.

Doing so prevents ESRP protocol data units (PDUs) from being dropped due to MAC address limit settings.

The following figure is an example of configuring a MAC address limit on a VLAN participating in an ESRP domain.

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MAC Address Limits and VLANs Participating in ESRP
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In the preceding figure, S2 and S3 are ESRP-enabled switches, while S1 is an ESRP-aware (regular Layer 2) switch. Configuring a MAC address limit on all S1 ports might prevent ESRP communication between S2 and S3. To resolve this, you should add a back-to-back link between S2 and S3. This link is not needed if MAC address limiting is configured only on S2 and S3, but not on S1.