let validar = {
    reg : /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/,
    campo : document.getElementById('ip'),
    validar : ()=> {
       validar.campo.value.match(validar.reg)?validar.campo.setAttribute('style','background-color: green')
       :validar.campo.setAttribute('style','background-color: red')
    },
    iniciar: ()=> validar.campo.addEventListener('keydown',()=>validar.validar())
}

validar.iniciar();