This read-only value reports the maximum number of Neighbor Binding Table entries the currently active IPv6 First-Hop Security policy allows for a single interface identifier, where -2 means no cap is enforced. It lets an administrator see the per-interface ceiling actually in force, which caps how many IPv6 neighbor bindings a busy interface can register and helps explain why binding entries might stop being learned. For example, if this value reads 50, an interface with 60 active IPv6 neighbors will only have the first 50 bindings tracked.