This read-create INTEGER, set per interface, holds the index of the IPv6-specific ACL applied to that interface's ingress traffic, with 0 meaning none applied. An admin uses this alongside, but separately from, the IPv4 ACL fields to filter incoming IPv6 traffic on a port, necessary as networks run dual-stack IPv4 and IPv6. For example, an admin blocking a specific IPv6 prefix from entering through a particular port would set this field to the index of an IPv6 ACL that denies that prefix.