# Hierarchical Policies for Interface Groups Overview

Hierarchical policies allow classifier groups and parent groups within a policy to point to line module global parent groups. The line module global parent groups (external parent groups) can point to other external parent groups. Full intra-interface policy hierarchies for all forwarding layer policies allow classified flows within a policy attachment to share bandwidth. Bandwidth-sharing between interfaces uses line module global parent group definitions and interface grouping. However, if you need to share bandwidth between two or more interfaces, rate-limits must be chained beyond a single attachment.

Policies for interface groups include external parent groups that are implicitly instantiated during policy attachment based on each unique interface group encountered.