Is 0.0.0.0 a valid IP address?

问题:

Is 0.0.0.0 a valid IP address? I want my program to be able to store it as an indication that no address is in use, but this won't work if it's actually valid.

回答1:

It's valid inasmuch as it contains four octets, each within the range 0 through 255 inclusive. However, it's not usable as a real IP address.

RFC1700 ^(a) states that 0.0.0.0/8 (0.<anything>.<anything>.<anything>) is reserved as a source address only. You can get into situation where it appears you have this address but that's normally because no address has been assigned to you (by DHCP, for example).

See also Wikipedia entry on IPv4.

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^(a) Although this RFC is now considered obsolete, it is still correct in terms of the given behaviour. Its replacement, https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml, still has the same text detailing use of the 0.0.0.0 address.

回答2:

Yes, it is an IP address but it is reserved.

0.0.0.0/8 - Addresses in this block refer to source hosts on "this" network. Address 0.0.0.0/32 may be used as a source address for this host on this network; other addresses within 0.0.0.0/8 may be used to refer to specified hosts on this network

回答3:

The 0.0.0.0 is used to bind all IPv4 interfaces. So it's a special value just like 127.0.0.1.

回答4:

Lets look at the Question being asked here by the OP.

Is 0.0.0.0 a valid IP address?

Yes. This is technically a valid IP address, and the other answers describe many various uses of it (I am not going to repost wikipedia links here ... or maybe I am).

As such I believe paxdiablo's answer above is the most correct, but lets look at the context of your question as well.

I want my program to be able to store it as an indication that no address is in use, but this won't work if it's actually valid.

This entirely depends on your use case. Given that this is a programmers forum, lets consider that perspective.

If your software is storing actual internet addresses - server locations, visitors to your website, replication/mirror or backup sites, web service or database servers etc. - then this will be perfectly valid. No machine on the internet will ever have this address assigned, nor will it ever resolve to a valid connection.

If on the other hand you are writing firewall or router firmware, then this address does take on special meaning; default route, accept any IP source/destination, block all IP source/destination, fall-trough catch-all, etc. as outlined by everyone else. However, let me point out that if you are coding on this level you should have a good enough understanding of network protocols so as to not need to ask this question in the first place.

I am therefore going to assume that most people viewing this question fall into the first category, and suggest that this is a perfectly valid way of storing a null, empty or missing IP address, if there is some reason that an actual null value cannot be used. Even if you neglect validation checking and your software does try to connect to this IP address, it will simply not be able to make a connection.

回答5:

It's reserved as the default route address.

It's common to see this via ipconfig when no address has been assigned to you.

回答6:

You can use it in your application to represent that it does not have an IP address, Microsoft also uses 0.0.0.0 when the machine has no IP address.

the "Valid" scenarios talked about above are dependent on the specific scenarios where they have nothing to do with your application.

回答7:

for all intents and purposes, yes. Each of the four numbers separated by the period have a value ranging from 0-255, so 0.0.0.0 is technically valid.

I don't think that there would be anyone in the world who actually has that IP though.

EDIT: okay, it is reserved for the default route, but it is still valid.

回答8:

of course it is. it will not be valid for a single host on a network however. it is in the broadcast range for the local network. read here: http://tools.ietf.org/html/rfc1700

回答9:

Doing a Network Whois query can also produce output that is quite helpful.
Example:
http://whois.arin.net/rest/nets;q=0.0.0.0?showDetails=true

Comment: The address 0.0.0.0 may only be used as the address of an outgoing packet when a computer is learning which IP address it should use. It is never used as a destination address. Addresses starting with "0." are sometimes used for broadcasts to directly connected devices.