It seems like the issue you encountered with the laptop not being able to connect back to the original network after being connected to a different one is likely due to the way domain authentication works in Windows environments. Let's break down your questions and provide some insights:
1. Connection Issue after Switching Networks:
When a computer is joined to a Windows domain, it establishes a trust relationship with the domain controller (DC) of that specific domain. When you moved the laptop to the second site and joined it to a different domain with a new DC, the trust relationship with the SBS 2011 domain controller at the first site was essentially broken.
2. Domain Authentication and Trust:
For a computer to authenticate against a domain controller, it needs to have a trust relationship with that specific domain. When you attempted to connect the laptop back to the original domain (SBS 2011), the broken trust would have prevented successful authentication.
3. Re-Joining the Domain:
Re-joining the laptop to the original domain (SBS 2011) essentially establishes a new trust relationship with the domain controller at the first site, allowing for proper authentication and network access.
4. Multiple Network Domain Access:
In Windows environments, a computer can only be directly joined to one domain at a time. While it's technically possible to switch between domains by disjoining and rejoining, as you experienced, it's not a seamless process and can lead to access issues like the one you encountered.
Summary:
- Normal Behavior: It is expected behavior that you had to rejoin the laptop to the original domain after connecting it to a different domain.
- Trust Relationships: Trust is established between a computer and a domain controller, and switching domains can break this trust.
- Single Domain Join: A PC can only be joined to one domain at a time, necessitating rejoining to switch between domains.
In your case, the laptop had to re-establish trust with the first domain to regain access to the network. Moving between domains in this way is not a common scenario and can lead to authentication issues as you described.