Why are underscores not allowed in host names or domain name?
我们在安装VC（VMware vCenter Server）的时候请勿将主机名中含有“_”符号，这将会导致web client无法注册到invetory当中。
If the vCenter Server host name contains an underscore, it is considered an invalid host name and that vCenter Server does not appear in the vSphere Web Client.
To resolve this issue, change the host name of the vCenter Server so that it does not contain any underscores.
If the host name is VCENTER_PROD, rename it to VCENTERPROD or another name without an underscore
Underscore in host name or domain name is not allowed.
bound up in this question:
- The keyboard of the Teletype (TTY) ASR-33 (a very common terminal interface of the period from whence this standard hails – I cut my computing teeth on one in grade school) doesn’t have underscore on it: which gives one a nasty problem: how do you type (input) a hostname if the hostname in question contains a character that your terminal interface can’t generate?
- software precedent (what the software of the day would accept),
- simplification to avoid confusion (it’s very easy to confuse dash and underscore)
- personal preference of the standards author (accepted by the community without objection).
互联网工程任务组-Internet Engineering Task Force (IETF)，成立于1985年底，是全球互联网最具权威的技术标准化组织，主要任务是负责互联网相关技术规范的研发和制定，当前绝大多数国际互联网技术标准出自IETF。