Validation ASP MVC 5

Question

public class HomeController : Controller
{
    private ProjetoFornecedorEntities db = new  ProjetoFornecedorEntities();
    // GET: Home
    public ActionResult Index(Fornecedor fornecedor)
    {

        return View(db.Fornecedor.ToList());
    }
    public ActionResult Create()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Create(Fornecedor fornecedor )
    {

            if (ModelState.IsValid)
            {


                db.Fornecedor.Add(fornecedor);
                db.SaveChanges();
                return RedirectToAction("Index");

            }

        return View("Create");
    }


}

Guys I’m going crazy already, my doubt is how not to duplicate fields at registration time for example ,I have a Cpf and can not register the same Cpf and as returns on screen,I searched and found the Remote but could not apply.