'Starts the proxy.'

def _start_proxy(self, ip=None, port=None, silent=False):

    if (not ip):
        ipport = self.pref.get_value('proxy', 'ipport')
        (ip, port) = ipport.split(':')
    self.w3af.mainwin.sb(_('Starting    local    proxy'))
    try:
        self.proxy = InterceptProxy(ip, int(port), self.w3af.uri_opener)
    except ProxyException as w3:
        if (not silent):
            self.show_alert(_(str(w3)))
        raise w3
    else:
        self.proxy.start()
