IP Addressing
CIDR Aggregator
Combine multiple subnets into minimal CIDR blocks. Optimize routing tables, firewall rules, and BGP announcements by reducing prefix count.
Input Subnets
Supports comma, semicolon, or newline separation
How to Use
- 1Enter your subnet list in CIDR notation (e.g., 10.0.0.0/24)
- 2Click "Aggregate" to combine into minimal CIDR blocks
- 3Copy the optimized list for your routing table or firewall rules
Aggregated Result
Enter subnets and click Aggregate
Common Use Cases
- Routing tables: Reduce route count for better performance
- Firewall rules: Consolidate ACLs and security policies
- BGP announcements: Minimize advertised prefixes
- IP allowlists: Simplify CDN or API access lists
Important Notes
- Aggregation may include IPs not in original list if ranges have gaps
- Only contiguous, power-of-2 aligned blocks can be combined
- Verify aggregated results match your security requirements
Aggregation Examples
| Input Subnets | Aggregated | Reduction |
|---|---|---|
| 192.168.0.0/24, 192.168.1.0/24 | 192.168.0.0/23 | 2 → 1 (50%) |
| 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24 | 10.0.0.0/22 | 4 → 1 (75%) |
| 172.16.0.0/24 through 172.16.255.0/24 | 172.16.0.0/16 | 256 → 1 (99.6%) |
| 10.1.0.0/24, 10.1.2.0/24 (gap at .1) | Cannot aggregate | Non-contiguous |
Aggregation Rules
- Contiguous: Subnets must be adjacent (no gaps)
- Aligned: Combined block must start at a valid boundary
- Power of 2: Result size must be 2ⁿ addresses
- Same prefix: Subnets being combined must share the same network prefix
Why Aggregate?
- Router memory: Fewer routes = lower TCAM usage
- Faster lookups: Smaller routing tables improve performance
- BGP stability: Fewer prefixes reduce churn and convergence time
- Cleaner configs: Easier to read and maintain
Related Articles
CIDR Notation Explained: From /8 to /32
A visual breakdown of CIDR blocks and what each prefix length actually means.
6 min readVLSM vs Equal-Size Subnets
When to use variable-length subnet masks and when equal subnets are better.
5 min readIPv4 Subnetting Reference Guide
Quick reference for subnet masks, CIDR notation, and usable host counts.
4 min read