Network address utilization

This is a measurement of the percentage of non-overlapping address space you consume out of all private address spaces available. VPCs are restricted to 65535 addresses, and data centers and offices have defined ranges. Networks are defined by Classless Inter-Domain Routing (CIDR) ranges that cannot overlap.

Network address utilization

Many AWS features use network addresses in subnets. Instances in an Auto Scaling group, load balancers (Classic Load Balancers or Application Load Balancers), and AWS Lambda can use a large number of addresses as load increases. Using very large subnets alleviates some of this problem, but can cause additional problems in network planning if you interconnect your private network spaces. You should keep track so you know if you need to add subnets to VPCs.

Plan your network and measure your utilization

• Identify CIDR ranges for VPCs, data centers, and office networks.
• Identify inter connectivity of private networks.
• Select system of record to store these ranges: database, Configuration Management Database (CMDB), etc.
• For AWS deployments:
  • Identify VPC CIDR ranges.
  • Identify deployments of automatically scaled instances and containers, load balancers, and AWS Lambda functions, map them to the respective subnets, and document the sizes of the subnets.
  • Estimate use of subnet addresses by allocated maximum size of Auto Scaling groups, between 8 and 128 load balancer instances for a Classic Load Balancer or Application Load Balancer per subnet, and the maximum concurrency of AWS Lambda functions, divided by the number of subnets.
  • Sum the total of each, along with other IP consuming services like NAT gateways, Network Load Balancers, RDS instances, etc.
• For data centers and office locations:
  • Identify physical data center and office location subnet CIDR ranges.
  • Identify the known or planned growth for the networks.
• Identify areas where there may not be enough network ranges available.
• Identify CIDR ranges that can be added to VPCs and physical networks.