How do sites share one IP plan?

VLANs belong to the whole organisation, and each subnet belongs either to one site or is shared by all of them. The usual pattern is one VLAN scheme with each site's own subnets: VLAN 10 Users might be 10.0.10.0/24 at head office and 10.1.10.0/24 at a branch.

• New subnets: creating a VLAN on a site gives the site its own subnet, even when another site already uses that VLAN number.
• Pickers: a site only offers its own subnets and the shared ones.
• The IPAM page (Settings → IPAM):
  • a Site filter
  • a By site summary
  • a column to move a subnet between sites
  • Add an address block, for the network's overall range (supernet) or a site's allocation
• The diagram assistant:
  • flags subnets that overlap anywhere in the network
  • warns when two sites use the same range, which is fine behind NAT but not on a routed WAN