服务器来初始地把该服务器的 host name 解析为地址. 客户端可以采用的替代 策略包括: 1) 将初始解析作为配置的一部分, 2) 使用基于 IP 的 URI 以及 HTTPS 对应的基于 IP 的证书, 或 3) 通过传统 DNS 或另一个 DoH 服务器解 析 DNS API 服务器的 hostname, 同时仍通过 HTTPS 对最终连接进行认证.
HTTP [RFC7230] 是一种无状态应用层协议, 因此 DoH 实现不在不同请求之间 提供有状态的顺序保证. DoH 不能用作要求严格排序的其他协议的传输.
DoH 服务器可以用任何有效 DNS 响应回答查询. 例如, 有效 DNS 响应可能在 DNS 头部中设置 TC (truncation) bit, 表示服务器无法为查询取回完整答案, 但提供了它能够获得的最佳答案. 对于无法满足的查询, DoH 服务器可以用 HTTP error 进行回复. 在同一示例中, DoH 服务器可以使用 HTTP error, 而不是使 用设置了 TC bit 的非错误响应.
多年来, 已经定义了许多使用 [RFC6891] 的 DNS 扩展. 特定于传输选择的扩 展, 例如 [RFC7828], 不适用于 DoH.
11. 参考文献
11.1. 规范性参考文献
[RFC1035] Mockapetris, P., "域名 - 实现和规范", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, https://www.rfc-editor.org/info/rfc1035.
[RFC2119] Bradner, S., "用于 RFC 中指示要求级别的关键词", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, https://www.rfc-editor.org/info/rfc2119.
[RFC2308] Andrews, M., "DNS 查询负缓存 (DNS NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, https://www.rfc-editor.org/info/rfc2308.
[RFC4648] Josefsson, S., "Base16, Base32 和 Base64 数据编码", RFC 4648, DOI 10.17487/RFC4648, October 2006, https://www.rfc-editor.org/info/rfc4648.
[RFC6265] Barth, A., "HTTP 状态管理机制", RFC 6265, DOI 10.17487/RFC6265, April 2011, https://www.rfc-editor.org/info/rfc6265.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., and D. Orchard, "URI 模板", RFC 6570, DOI 10.17487/RFC6570, March 2012, https://www.rfc-editor.org/info/rfc6570.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "超文本传输协议 (HTTP/1.1): 消息语法和路由", RFC 7230, DOI 10.17487/RFC7230, June 2014, https://www.rfc-editor.org/info/rfc7230.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "超文本传输协议 (HTTP/1.1): 语义和内容", RFC 7231, DOI 10.17487/RFC7231, June 2014, https://www.rfc-editor.org/info/rfc7231.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "超文本传输协议 (HTTP/1.1): 条件请求", RFC 7232, DOI 10.17487/RFC7232, June 2014, https://www.rfc-editor.org/info/rfc7232.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "超文本传输协议 (HTTP/1.1): 缓存", RFC 7234, DOI 10.17487/RFC7234, June 2014, https://www.rfc-editor.org/info/rfc7234.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "超文本传输协议 (HTTP/1.1): 认证", RFC 7235, DOI 10.17487/RFC7235, June 2014, https://www.rfc-editor.org/info/rfc7235.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "超文本传输协议 第 2 版 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, https://www.rfc-editor.org/info/rfc7540.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: HTTP/2 的头部压缩", RFC 7541, DOI 10.17487/RFC7541, May 2015, https://www.rfc-editor.org/info/rfc7541.
[RFC7626] Bortzmeyer, S., "DNS 隐私考虑", RFC 7626, DOI 10.17487/RFC7626, August 2015, https://www.rfc-editor.org/info/rfc7626.
[RFC8174] Leiba, B., "RFC 2119 关键词中大写与小写的歧义", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, https://www.rfc-editor.org/info/rfc8174.
[RFC8446] Rescorla, E., "传输层安全 (TLS) 协议 1.3 版", RFC 8446, DOI 10.17487/RFC8446, August 2018, https://www.rfc-editor.org/info/rfc8446.
11.2. 资料性参考文献
[FETCH] "Fetch 动态标准", August 2018, https://fetch.spec.whatwg.org/.
[RFC2818] Rescorla, E., "HTTP over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, https://www.rfc-editor.org/info/rfc2818.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 公钥基础设施证书 和证书吊销列表 (CRL) 配置文件", RFC 5280, DOI 10.17487/RFC5280, May 2008, https://www.rfc-editor.org/info/rfc5280.
[RFC5861] Nottingham, M., "用于陈旧内容的 HTTP Cache-Control 扩展", RFC 5861, DOI 10.17487/RFC5861, May 2010, https://www.rfc-editor.org/info/rfc5861.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van Beijnum, "DNS64: 用于从 IPv6 客户端到 IPv4 服务器网络地址转换 的 DNS 扩展", RFC 6147, DOI 10.17487/RFC6147, April 2011, https://www.rfc-editor.org/info/rfc6147.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "DNS 扩展机制 (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/RFC6891, April 2013, https://www.rfc-editor.org/info/rfc6891.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba, "DNS 中应用特性的架构考虑", RFC 6950, DOI 10.17487/RFC6950, October 2013, https://www.rfc-editor.org/info/rfc6950.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, "X.509 Internet 公钥基础设施 在线证书状态协议 - OCSP", RFC 6960, DOI 10.17487/RFC6960, June 2013, https://www.rfc-editor.org/info/rfc6960.