最近在找支持 DNSSEC 的解析商，发现大部分解析商都已经支持了，但国内的阿里云和 dnspod 都是付费才支持，不过很多国外的解析商是免费提供的，比如：

cloudflare 免费套餐支持

gandi 买域名就送解析服务，DNSSEC 不需要额外付费

vultr 不需要购买主机，免费服务

desec 非盈利组织，宣称有 Anycast Networks

在设置 SRV 记录时，我发现阿里云和 dnspod 都不支持设置记录值为 0 0 0 .，也就是 target 不能为 .

但根据 RFC 2782：

   Target         The domain name of the target host.  There MUST be one or more         address records for this name, the name MUST NOT be an alias (in         the sense of RFC 1034 or RFC 2181).  Implementors are urged, but         not required, to return the address record(s) in the Additional         Data section.  Unless and until permitted by future standards         action, name compression is not to be used for this field.          A Target of "." means that the service is decidedly not         available at this domain. 

你要问我为什么要这样设置，RFC 6186：

   In addition, with SRV RRs it is possible to indicate that a    particular service is not supported at all at a particular domain by    setting the target of an SRV RR to ".".  If such records are present,    clients MUST assume that the specified service is not available, and    instead make use of the other SRV RRs for the purposes of determining    the domain preference.     Example: service records for IMAP and POP3 with both TLS and non-TLS    service types are present.  Both IMAP and POP3 non-TLS service types    are marked as not available.  IMAP (with TLS) has a lower-numbered    priority value 0 than POP3 (with TLS) at priority 10, indicating to    the MUA that IMAP is preferred over POP3, when the MUA can support    either service, and only the TLS versions of the services are    available.         _imap._tcp     SRV  0 0 0   .        _imaps._tcp    SRV  0 1 993 imap.example.com.        _pop3._tcp     SRV  0 0 0   .        _pop3s._tcp    SRV 10 1 995 pop3.example.com. 

给阿里云提了工单，并附上 RFC，结果反馈我

您好，抱歉让您久等了，和后端确认目前阿里云的云解析，目前云解析暂不支持目标地址为“.”的 srv 记录解析。目前云解析这边暂无替代方案。如果您一定要添加这种解析，只能建议您考虑使用其他支持的平台来配置了。 

刚刚又给腾讯云提了工单，还没有回复

RFC 6186 不看也就罢了，毕竟是关于 Use of SRV Records for Locating Email Submission/Access Services 的，但 RFC 2782 是关于 SRV 记录的 RFC，里面详细描述了 SRV 记录的格式，设计校验时都不看一下的吗？

不过我上面列出的国外解析商倒是都支持，果然国内的云平台把用户当傻子，什么都要校验一下