Simply

    "allowed_connections": {
        "192.168.1.10": [1200, 1201, 1202],
        "192.168.1.12": [1200, 1201, 1202],
        "192.168.1.11": [1000, 1003]
    }

Or, with the second proposal (I'm not sure if it's possible)

    "allowed_connections": {
        ["192.168.1.10", "192.168.1.12"]: [1200, 1201, 1202],
        ["192.168.1.11"]: [1000, 1003]
    }