iACLs, or infrastructure access control lists, are network ACLs designed to protect routers, switches, firewalls, and other control-plane systems. Instead of filtering general user traffic, they permit only the specific management and routing traffic that infrastructure devices need to function, such as SSH from admin networks, routing protocol peers, or monitoring systems.
In cyber security, iACLs matter because control-plane devices are high-value targets. If attackers can reach management interfaces or internal services that should be hidden, they may exploit vulnerabilities, brute-force credentials, or move laterally into the administrative layer. Tight iACLs reduce that exposure by denying everything by default and allowing only trusted sources and ports. Defenders use them as a hardening measure before and after patching, especially for internet-facing or segmented enterprise networks. They are not a replacement for fixing bugs, but they can slow exploitation and limit what an attacker can touch if a device is probed or compromised.