The consistency principle states that systems are more usable and learnable when similar parts are expressed in similar ways [Lidwell 2010]. Consistency can be in appearance (e.g. network documentation) or in function (e.g. device configuration). Internal consistency refers to consistency with other components in the system (e.g. DHCP allocates the same address range in all subnets). External consistency refers to consistency with outside elements (e.g. VLAN100 has the same functions in all branches of the organization).
The consistency principle can be applied in network design in many ways:
- Use templates in device configuration to reduce human errors and reduce the effort of management and troubleshooting.
- Use consistent firewall policies in all firewalls.
- Apply consistency in designing IP addressing scheme, VLAN to IP addresses mapping, and component labeling conventions.
- Apply consistency in network documentation (symbols, icons, drawing sizes, etc.)
Consistency should be used without compromising functionality. Existing design standards and best practices should be followed whenever possible.
Read about other Network Design Principles.