This read-only value reports the maximum number of hosts this port's hardware is actually capable of supporting under port security. An admin checks this hardware ceiling before setting portSecurityMaxHost, since a portSecurityMaxHost value larger than this capability effectively removes the host-count limit entirely. For example, seeing portSecurityMaxHostCapability=64 on a port tells the admin they cannot meaningfully cap that port below or at 64 learned hosts using the hardware's real limit.