什么是最小的有效域名? [英] What is smallest valid domain name?

问题描述

从技术上讲，什么是有效域名

Just curious technically what is valid domain name

t. <- is that valid

localhost is valid

我记得读的东西很短，甚至没有两个单词

I remember reading something very short without even two words

推荐答案

其他答复已经为您提供了一些提示，但我认为由于您的问题含糊其辞，因此缺少将两种情况分开的提示.

The other replies give you already some hints but I think they lack to separate two cases because your question is vague.

实际上我看到3点:

• 根据DNS语法规则，什么在技术上有效?
• 今天在IANA根上可以做什么工作?
• 如今，像浏览器这样的最终客户有什么用?

第一个点由 Calle Dybedahl 覆盖，从技术上讲.是最小的标签(或空标签被显示为点).但这本身并不是很有用.

The first point is covered by Calle Dybedahl, technically . is the smallest label (or the empty label being diplayed as a dot). But this is not very useful just by itself.

要完成此操作，主机名的每个标签长度为1到63个字符.您只能在字母，数字和连字符之间进行选择.以前，标签不能以数字开头，但是很早以前就取消了此限制(否则将不能使用3com.com).但是，标签的限制仍然没有以连字符开头.因此，您可以使用1个字符的标签/名称/域名作为任何字母(例如"ASCII"字母，仅从"a"到"z"，不区分大小写)或数字. 因此这在技术上是有效的，并且在某些实验室实验中，您可以控制根区域. (以上所有内容均由 RFC952 覆盖，然后由

To complete, each label of an hostname is 1 to 63 characters long. You can only choose between letters, digits and hyphen. Previously a label could not start with a digit but this restriction has been lifted long ago (otherwise 3com.com would not be possible). However the restriction remains of a label not starting with hyphen. So you can have a 1 character label/name/domain name being any letter (as in "ASCII" letters that is exclusively 'a' to 'z', case insensitive) or digit. So this would be technically valid and in some lab experiment where you control the root zone you could have that. (all the above is covered by RFC952 first and then amended by RFC1123 to remove restriction on first digit; they may be terse documents to read, a gentler introduction would be on Hostname entry in Wikipedia). Note that there is a subtle distinction between hostnames and names in the DNS in general: a hostname is a name in a DNS but not all names are hostnames, as technically a name can have any byte content, whereas an hostname is restricted by the rules above (and is mostly what people will see in their day to day life on the Internet, where other names serve other infrastructure purposes)

现在，第二点是当前IANA根及其今天的内容.今天没有一个人物的名字，我怀疑会有一天. 它以2个字母长的ccTLD开始.有一个添加新gTLD的过程，但它们的长度基本上至少为3个字符(比IDN的复杂得多，IDN可能有带有1个或2个代码点的标签，但通过IDNA规则，这将是一个xn--标签，因此在DNS中看到的长度超过4个字符). 另外，今天的IANA根目录中也不存在所有两个字符组合，因为它们都是ccTLD，因此在获取其列表时必须代表当前"国家(而不是ISO)国家/地区名称列表(ISO 3166). -1 Alpha2)

Now, second point, the current IANA root and its content today. There are no one character names there today and I doubt there will be one day. It starts with ccTLDs being 2 letters long. There is a process to add new gTLDs but they are basically at least 3 characters long (a little more complicated than that for IDNs, where there could be labels with 1 or 2 codepoints but through IDNA rules this will be a xn-- label so more than 4 characters long as seen in the DNS). Also, not all two characters combinations are existing in the IANA root today, as they are ccTLDs, and hence must represent "current" country as their list is taken, loosely (they are exceptions) from the ISO list of country names (ISO 3166-1 Alpha2)

没有人能预测会发生什么，但是至少今天没有一个字符TLD上的应用空间.

Noone can predict what would happen, but at least there is no space today for applications on one character TLDs.

tadman 答复涵盖了这一点以及相关的第三点，即今天有效. 实际上，作为一个或两个字符的TLD，您可能会看到相同的问题，通常被称为无点域".例如，解析https://dk/的原因是与.DK TLD相关的A/AAAA记录到标签.dk. 对于ccTLD而言，这是可能的，但对于gTLD而言，这是不可能的，因为ICANN强烈反对基于各种原因的理由，其中之一是它们的运行不佳，请参阅此报告以获取详细信息: https://www.icann.org/en/system/files/files/sac-053-en.pdf 请注意，它们不会因DNS协议中的问题而工作不佳，只是因为如果输入没有足够"的点，则使用各种最终客户端OS/应用程序自动附加域名后缀(或多个)，即对于无点域名肯定是正确的.

tadman reply covered this point a little and the associated third point, what works today. In fact, being one or two characters TLD you could see the same problem, often described as "dotless domain". For example https://dk/ resolves because the .DK TLD associated A/AAAA records to the label .dk. This is possible in ccTLDs but not for gTLDs, as ICANN is strongly against that based on different reasons, one among them is that they work poorly, see this report for details: https://www.icann.org/en/system/files/files/sac-053-en.pdf Note that they do not work poorly because of problems in the DNS protocol, just because various end clients OS/applications are used to automatically append a domain name suffix (or more than one) if the input has not "enough" dots, which is certainly true for a dotless domain name.

请参见 RFC 7085已经无点的顶级域" (2013年12月)列出了当时所有的无点"案件，例如.DK，但还有15个.如果您计算对MX DNS类型的答复，甚至更多.

See RFC 7085 "Top-Level Domains That Are Already Dotless" (December 2013) for a listing of all "dotless" cases (at that time), such as .DK, but they were 15 more. And even more if you count replies for MX DNS type.

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