Cisco APIC Layer 2 Networking Configuration Guide, Release 6.2(x)

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Cisco APIC Layer 2 Networking Configuration Guide, Release 6.2(x)

Overlapping VLAN validation

Updated: July 7, 2026

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Describes a global feature that prevents association of overlapping VLAN pools on a single EPG to ensure network stability and prevent connectivity issues.

Overlapping VLAN validation is a global feature that

  • prevents association of overlapping VLAN pools on a single EPG

  • blocks configuration when a domain contains a VLAN pool with a range overlapping with another domain already associated to the EPG, and

  • ensures deterministic FD VNID allocation across switches to prevent connectivity issues.

Feature behavior and requirements

The overlapping VLAN validation feature has specific enablement requirements and operational behavior:

  • If there are any overlapping pools allocated with any EPG in APIC, then this feature cannot be enabled (an error is displayed if there is an attempt to enable it).

  • If no existing overlapping pools are present, then this feature can be enabled.

  • Once enabled, when an attempt to allocate a domain on an EPG is performed, and the domain contains a VLAN pool with a range overlapping with another domain already associate to the EPG, then the configuration is blocked.

When overlapping VLAN pools exist under an EPG, network issues can occur:

  • The FD VNID allocated for the EPG by each switch is non-deterministic and different switches may allocate different VNIDs.

  • This can cause EPM sync failures between leaf switches within a vPC domain (causing intermittent connectivity for all endpoints within the EPG).

  • It can also cause bridging loops if user is extending STP between the EPG, as the BPDUs will be dropped between switches due to FD VNID mismatch.