Your ASN is already in use. Please enter a new ASN or delete all existing MCC resources associated with this ASN to unlock it.

The error indicates that ASN 134712 is already associated with existing MCC (Microsoft Connected Cache or related) resources, and Azure requires those resources to be removed before the ASN can be reused for a new Operator Verification.

From the available commands and APIs:

1. Use Azure Peering/MCC management tools to locate existing ASN usage
   • If managing peering via Azure CLI, list or inspect peer/registered ASNs to confirm where ASN 134712 is in use.
   • For example, if the ASN is registered under a peering resource, az peering asn show can be used when the peer ASN name is known:

          az peering asn show --peer-asn-name <peer-asn-name>
     

   • For registered ASNs under a specific peering, use:

          az peering registered-asn show \
            --resource-group <resource-group> \
            --peering-name <peering-name> \
            --registered-asn-name <registered-asn-name>
     

   • These commands help identify which peering/MCC resources are currently bound to ASN 134712.
2. Remove the existing ASN association if it belongs to the same subscription/tenant
   • Once the relevant peer ASN object is identified, it can be deleted with Azure CLI:

          az peering asn delete --peer-asn-name <peer-asn-name>
     

   • This frees the ASN so that it can be reused in the MCC Operator Verification flow.
   • Be aware that deleting a peer ASN or related peering resource can impact existing peering or MCC traffic; ensure that no production dependency remains before deletion.
3. If the ASN is tied to another tenant or unknown MCC resources
   • If the ASN is in use under a different Azure subscription/tenant or by legacy/unknown MCC resources that cannot be managed directly, this must be handled by Microsoft support.
   • Open a support ticket from the Azure Portal under the subscription used for MCC/Peering, providing:
     • ASN: 134712
     • ISP/Operator name (Pipex Network)
     • The exact error message from MCC Operator Verification
     • Any proof of ASN ownership (for example, RIR registration details)
   • The support team can locate and remove or unlock any stale or conflicting MCC resources associated with ASN 134712 on the backend.
4. Ensure ASN and prefix requirements are met
   • When re-registering the ASN and associated prefixes for Azure Peering/MCC, ensure that all technical requirements are satisfied so validation succeeds:
     • Prefixes must not be in private ranges.
     • The origin ASN must be registered in a major routing registry.
     • Prefixes must be announced from all required peering sessions.
     • Routes must carry the Peering Service community 8075:8007.
     • AS paths must not exceed length 3 and must not contain private ASNs or AS prepending.

Once the conflicting MCC/peering resources are removed or unlocked by either direct management (CLI) or Microsoft support, rerun the MCC Operator Verification using ASN 134712.

References:

• az peering asn delete
• az peering asn show
• az peering registered-asn show
• Peering registered prefix requirements
• PeerAsn interface