Explanation
Step 1: user subscriptions
If you want to delete a quota, you must work back through any plans and offers that use that quota. Starting with the offers, ensure they have no subscriptions, delete each offer, then delete the plans that use the quota, and so on.
Step 2: offers
Deleting an offer is only possible if there are no subscriptions that belong to that offer.
Step 3: plans
You can't delete a quota if there are any current plans that use it. You must first delete the plan that references the quota.
Reference:
https://learn.microsoft.com/en-us/azure-stack/operator/azure-stack-delete-offer

Explanation
Box 1: BGP
BGP routing
Using a dynamic routing protocol like BGP guarantees that your system is always aware of network changes and facilitates administration. For enhanced security, a password may be set on the BGP peering between the TOR and the Border.
Box 2: Layer 3 uplinks with point-to-point connectivity
To integrate Azure Stack Hub to the network it requires uplinks from the Top-of-Rack switches (ToR) to the nearest switch or router, which on this documentation is referred as Border. The ToRs can be uplinked to a single or a pair of Borders.
The top of rack (TOR) switches require Layer 3 uplinks with Point-to-Point IPs (/30 networks) configured on the physical interfaces. Layer 2 uplinks with TOR switches supporting Azure Stack Hub operations isn't supported Reference:
https://learn.microsoft.com/en-us/azure-stack/operator/azure-stack-border-connectivity
https://learn.microsoft.com/en-us/azure-stack/operator/azure-stack-network

Explanation
Box 1: Microsoft legacy Cryptographic Service Provider (CSP) key provider Give an app access to Azure Stack Hub resources An application that deploys or configures resources through Azure Resource Manager must be represented by its own identity, known as a security principal. Just as a user is represented by a user principal, an app is represented by a service principal.
Create an app registration that uses a certificate credential
When creating a certificate credential, the following requirements must be met:
* The cryptographic provider must be specified as a Microsoft legacy Cryptographic Service Provider (CSP) key provider.
* The certificate format must be in PFX file, as both the public and private keys are required. Windows servers use .pfx files that contain the public key file (TLS/SSL certificate file) and the associated private key file.
* Etc.
Box 2: .pfx
Reference: https://learn.microsoft.com/en-us/azure-stack/operator/give-app-access-to-resources