使用XmlDocument时跳过DTD验证

读取xml时出现System.Net联网网络错误

XmlReaderSettings xs = new XmlReaderSettings();
xs.XmlResolver = null;
xs.DtdProcessing=DtdProcessing.Ignore;//xs.ProhibitDtd = false;
XmlReader reader = XmlReader.Create(url, xs);
XmlDocument doc = new XmlDocument();