Does the OSPF area ID need to be unique within the Autonomous System (AS)?

In OSPF (Open Shortest Path First), the area ID does not need to be unique within the Autonomous System (AS). This means that the same area ID can be used across different areas as long as they belong to different ASes. OSPF is designed to allow flexibility in network design, meaning that different OSPF instances can share the same area IDs independently of one another without causing issues.

This is significant for network segmentation and design. It enables network engineers to leverage existing configurations or established naming conventions when setting up new OSPF instances without having to devise entirely new area IDs. For example, if an organization has multiple ASes for different business units, they can use familiar area IDs across different ASes without any conflicts arising from this duplication.

In contrast, area IDs must be unique within a particular OSPF instance, and specificity regarding certain types of areas does not change the fundamental requirement of uniqueness within that instance. Also, since area IDs are primarily a function of configuration practice and design, the concern about uniqueness applies more to OSPF instances than to the AS level as a whole.