blocks|key|3018553|text|任何正确的TCP/IP实现都将保留地址127.0.0.1以引用本地计算机。但是，名称"localhost“到该地址的映射通常依赖于系统hosts文件。如果要从hosts中删除本地主机条目，则本地主机名称可能根本无法正确解析。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3018554|entityMap^0|1V|5|27|5|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

Any correct implementation of TCP/IP will reserve the address 127.0.0.1 to refer to the local machine. However, the mapping of the name "localhost" to that address is generally dependent on the system <code>hosts</code> file. If you were to remove the localhost entry from <code>hosts</code>, then the localhost name may no longer resolve properly at all.

blocks|key|3018760|text|在任何IP堆栈中都为本地主机保留了127.0.0.1。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3018761|"localhost“作为主机名是而不是保证会在那里。如果主机/DNS设置配置错误，localhost将无法解析。|offset|length|style|BOLD|3018762|debian机器上的例子：|3018763|topaz:/root#+vi+/etc/hosts
[comment+out+localhost+entry]

topaz:/root#+ping+localhost+
ping:+unknown+host+localhost|code-block|syntax|javascript|3018764|entityMap^0|0|H|3|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|U|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|V|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

127.0.0.1 is reserved in any IP stack for the local host.

"localhost" as a host name is not guaranteed to be there. If the host/DNS settings are misconfigured, localhost will not resolve.

Example on a debian box:

<pre><code>topaz:/root# vi /etc/hosts
[comment out localhost entry]

topaz:/root# ping localhost 
ping: unknown host localhost
</code></pre>

blocks|key|762786|text|不是的。首先，localhost是一种约定，而不是规则。大多数情况下，它是默认设置的，但没有任何强制要求。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|762787|其次，没有什么可以说你总是可以ping+127.0.0.1。作为示例(在unix系统上)，请尝试执行以下操作：|762788|sudo+ifconfig+lo+down+ping+127.0.0.1|762789|正如cruizer所说，127.0.0.1+(如果存在)被定义为本地计算机。但它并不一定要存在。|762790|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/113293/is-the-host-localhost-always-available-for-the-own-system#113302^0|7|9|0|0|0|L|M|E|0|2|7|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|12|8|@]|D|@$9|13|A|14|1|15]]|E|$]]|$1|L|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

No.
For a start <code>localhost</code> is a convention rather than a rule. Mostly it's set by default, but there's nothing to mandate it.

Secondly, there's nothing to say that you can always ping 127.0.0.1.
As an example (on a unix system) try the following:

<code>sudo ifconfig lo down</code>
<code>ping 127.0.0.1</code>

As <a href="https://stackoverflow.com/questions/113293/is-the-host-localhost-always-available-for-the-own-system#113302">cruizer</a> said, 127.0.0.1 (if it exists) is defined to be the local machine. But it doesn't have to exist.

blocks|key|762821|text|学究的答案(对不起，格雷格:)是读RFC+3330|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|762822|+++127.0.0.0/8+-+This+block+is+assigned+for+use+as+the+Internet+host
+++loopback+address.++A+datagram+sent+by+a+higher+level+protocol+to+an
+++address+anywhere+within+this+block+should+loop+back+inside+the+host.
+++This+is+ordinarily+implemented+using+only+127.0.0.1/32+for+loopback,
+++but+no+addresses+within+this+block+should+ever+appear+on+any+network
+++anywhere+[RFC1700,+page+5].|code-block|syntax|javascript|762823|(上面的“通常”应该理解为“经常”-大多数当前的操作系统都支持使用所有127.0.0.0/8作为环回。)|762824|关于"localhost“是否总是解析到127.0.0.1+-他是正确的，它通常是相同的，但技术上特定于实现：|762825|~>+dig+localhost.t...e.org

...

;;+ANSWER+SECTION:
localhost.t...e.org.+86400+IN++++A+++++++127.0.0.2|762826|entityMap|0|LINK|mutability|MUTABLE|url|http://www.faqs.org/rfcs/rfc3330.html^0|H|8|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|F|7|13|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

The pedantic answer (sorry, Greg :), is to read <a href="http://www.faqs.org/rfcs/rfc3330.html" rel="nofollow noreferrer">RFC 3330</a>:

<pre><code> 127.0.0.0/8 - This block is assigned for use as the Internet host
 loopback address. A datagram sent by a higher level protocol to an
 address anywhere within this block should loop back inside the host.
 This is ordinarily implemented using only 127.0.0.1/32 for loopback,
 but no addresses within this block should ever appear on any network
 anywhere [RFC1700, page 5].
</code></pre>

(The "ordinarily" above should probably be read as "often" - most current operating systems support using all of 127.0.0.0/8 as loopback.)

With regards to whether "localhost" always resolves to 127.0.0.1 - he is correct, it's generally the same, but technically implementation specific:

<pre><code>~&gt; dig localhost.t...e.org

...

;; ANSWER SECTION:
localhost.t...e.org. 86400 IN A 127.0.0.2
</code></pre>

blocks|key|3019231|text|如果您的客户端连接到的DNS服务器遵循rfc1912，那么是的，localhost应该解析为127.0.0.1。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3019232|RFC1912
4.1
...
+++Certain+zones+should+**always+be+present**+in+nameserver+configurations:
+++++++++++primary+++++++++localhost+++++++++++++++localhost
+++++++++++primary+++++++++0.0.127.in-addr.arpa++++127.0
...
+++The+"localhost"+address+is+a+"special"+address+which+always+refers+to
+++the+local+host.++It+should+contain+the+following+line:

+++++++++++localhost.++++++IN++++++A+++++++127.0.0.1

+++The+"127.0"+file+should+contain+the+line:

+++++++++++1++++PTR+++++localhost.|code-block|syntax|javascript|3019233|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If the DNS servers your client is connected to is following rfc1912 then yes, localhost should resolve to 127.0.0.1.

<pre><code>RFC1912
4.1
...
 Certain zones should **always be present** in nameserver configurations:
 primary localhost localhost
 primary 0.0.127.in-addr.arpa 127.0
...
 The "localhost" address is a "special" address which always refers to
 the local host. It should contain the following line:

 localhost. IN A 127.0.0.1

 The "127.0" file should contain the line:

 1 PTR localhost.
</code></pre>

blocks|key|5274983|text|我认为对于大多数平台，localhost几乎解析为127.0.0.1，但所有以127...*开头的IP也解析为localhost。尝试pinging+127.255.255.254，它仍然会响应。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5274984|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I think localhost pretty much resolves to 127.0.0.1 for most platforms but all IPs that start with 127...* resolve to localhost as well. Try pinging 127.255.255.254 and it'll still respond.

blocks|key|3018648|text|从理论上讲，有些情况下它可能并不存在。在实践中，它总是存在的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3018649|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In theory, there are cases where it might not exist. In practice, it's always there.

blocks|key|3019346|text|像样的防火墙也允许您过滤环回接口上的访问。因此，可以设置一个防火墙规则来丢弃发往本地主机(127.0.0.1)的icmp+ping数据包。此外，正如其他每个人已经提到的，甚至不能保证本地主机或127.0.0.1地址和环回接口的存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3019347|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Decent firewalls allow you to filter access on the loopback interfaces too. So, it's possible to set up a firewall rule that drops icmp ping packets going to localhost (127.0.0.1). Also, as everyone else has already mentioned, even the existence of the localhost or 127.0.0.1 address and the loopback interface isn't guaranteed.

blocks|key|3864104|text|答案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3864105|通常称为“环回”的127.0.0.1是必需的。尽管你的计算机可能会让你做一些愚蠢的事情，比如禁用它，或者在物理接口上配置该范围，但这些都是无效的。|3864106|"+localhost“只是一个主机名，按照惯例，它应该是127.0.0.1作为系统管理员或主机管理员，您应该避免允许localhost指向其他地址的配置。|3864107|您不应该编辑您的主机文件来更改"localhost“的地址。您应该将您的域配置为具有本地主机。和指向127.0.0.1的localhost.domain.com条目。|3864108|您不应该让代理服务器响应"+localhost“或任何以localhost开头的FQDN。|3864109|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

The answer is: 

127.0.0.1, often referred to as the "loopback", is required. Although your computer might let you do silly things, like disable it, or configure that range on a physical interface, these are all invalid.

"localhost" is just a hostname, which by convention, should be 127.0.0.1 As a system administrator or hostmaster, you should avoid configurations that allow localhost to point to other addresses. 

You should not edit your hosts file to change the address of "localhost". You should configure your domains to have a localhost. and localhost.domain.com entry that points to 127.0.0.1.

You should not let your proxy servers respond to "localhost" or any FQDN that starts with localhost.

blocks|key|5275066|text|好的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5275067|解析的原因是记录在%25WINDOWS_DIR%25\System32\drivers\etc\hosts文件中，如下所示：|5275068|127.0.0.1本地主机|5275069|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Ok. 

The reason why it resolves it is record in %WINDOWS_DIR%\System32\drivers\etc\hosts file like this:

127.0.0.1 localhost

Is it always possible to ping localhost and it resolves to 127.0.0.1?

I know Windows Vista, XP, Ubuntu and Debian do it but does everyone do it?

Is the host localhost always available for the own system?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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是否总是可以ping通localhost并将其解析为127.0.0.1？我知道Windows Vista，XP，Ubuntu和Debian都这样做，但是每个人都这样做吗？

问主机localhost是否始终可用于自己的系统？
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