What are Aliases?
Aliases in OPNsense are named groups of IP addresses, subnets, ports, or hostnames. Instead of writing separate rules for 20 servers, you write one rule referencing an alias containing all 20 IP addresses.
Performance Benefits
Modern firewalls compile rules into lookup tables (like `pf` tables in BSD). Using aliases:
1. **Reduces CPU Overhead**: Single rules matching against dynamic tables are significantly faster than hundreds of individual rules.
2. **Prevents Memory Bloat**: Aliases allow the firewall engine to reuse table structures efficiently.
Types of Aliases in OPNsense
- **Host(s)**: Group of single IPs.
- **Network(s)**: Group of CIDR subnets.
- **Port(s)**: Group of TCP/UDP port numbers.
- **URL Table (IPs)**: Automatically fetches IP lists from a remote server (ideal for threat feeds).