Which design concern should be accounted for in all Layer 3 virtualization technologies?

Layer 3 redundancy is an availability concern applicable to many designs but is not a constraint uniquely introduced or universally required by all Layer 3 virtualization technologies.

Layer 3 virtualization technologies such as GRE, IPsec, and MPLS all append additional header bytes to the original IP packet, which reduces the effective MTU available for the payload. If the encapsulated packet exceeds the path MTU, fragmentation occurs, causing performance degradation or silent drops when the DF bit is set. Packet sizing must be explicitly accounted for in every L3 virtualization design to ensure correct MTU handling end to end.

Application usage is a traffic engineering consideration but is not a fundamental design constraint that applies uniformly across all Layer 3 virtualization technologies.

Layer 3 stability relates to routing protocol behavior and convergence and is not a concern that is uniquely introduced by Layer 3 virtualization technologies.