This read-write INTEGER (unspecified(-1), perimeter(1), internal(2)) in the Neighbor Binding Integrity policy table specifies whether ports/VLANs using this policy sit at the untrusted network edge or inside the trusted core. An admin cares because perimeter ports get the strictest binding-integrity checks (since they face potentially hostile hosts), while internal ports can be treated more permissively. For example, setting this to perimeter(1) for policy "nbi-edge" on user-facing access ports applies the tighter edge-facing checks there, while core uplinks would use internal(2).