A company already uses the address space 10.20.0.0/16 for a hub virtual network and 10.21.0.0/16 on-premises. A new spoke virtual network will be peered to the hub and may later connect to the on-premises network. Which address space should the administrator choose for the spoke to avoid future routing conflicts?
This range does not overlap with either the hub VNet or the on-premises network. It also provides a full /16, which leaves enough room for multiple subnets and future growth while keeping peering and hybrid connectivity straightforward.
Why this answer
Option C (10.22.0.0/16) is correct because it is a unique, non-overlapping address space that does not conflict with the existing hub VNet (10.20.0.0/16) or the on-premises network (10.21.0.0/16). When a spoke VNet is peered to the hub and later connected to on-premises via VPN or ExpressRoute, Azure requires that all peered and connected address spaces be unique to avoid routing conflicts. Choosing a completely separate /16 ensures no future overlap.
Exam trap
The trap here is that candidates often assume any address space outside the hub's /16 is safe, but they forget to check for overlap with the on-premises network (10.21.0.0/16) or incorrectly think that a smaller subnet within the hub's range (like 10.20.64.0/19) can be used if it is not currently in use, ignoring that Azure requires completely non-overlapping ranges for peered VNets.
How to eliminate wrong answers
Option A (10.20.64.0/19) is wrong because it falls within the hub VNet's 10.20.0.0/16 range, causing an immediate IP address overlap that would prevent VNet peering from succeeding. Option B (10.21.0.0/16) is wrong because it exactly matches the on-premises address space, which would create a routing conflict when the spoke later connects to on-premises (Azure cannot distinguish between the on-premises network and the spoke VNet). Option D (10.20.128.0/17) is wrong because it is a subset of the hub's 10.20.0.0/16, overlapping with the hub VNet and breaking peering due to non-unique address ranges.