CODEWITHSUNDEEP
socketsnetwork-programmingdnslocalhost
Bohemian
Bohemian

Reputation: 425448

What is the difference between 127.0.0.1 and localhost

Assuming the following is defined in .../hosts:

127.0.0.1 localhost

What, if any, are the actual differences between using 127.0.0.1 and localhost as the server name, especially when hitting processes running locally that are listening for connections?

Upvotes: 237

Views: 198794

Answers (5)

Wayne Walker
Wayne Walker

Reputation: 2466

Some applications will treat localhost specially.

For example, the MySQL client will treat localhost as a request to connect to the local Unix domain socket instead of using TCP to connect to the server on 127.0.0.1. This may be faster, and may be in a different authentication zone.

Upvotes: 42

The Mask
The Mask

Reputation: 17477

Well, by IP is faster.

Basically, when you call by server name, it is converted to original IP.

But it would be difficult to memorize an IP, for this reason the domain name was created.

Personally I use http://localhost instead of http://127.0.0.1 or http://username.

Upvotes: 11

paxdiablo
paxdiablo

Reputation: 882806

Well, the most likely difference is that you still have to do an actual lookup of localhost somewhere.

If you use 127.0.0.1, then (intelligent) software will just turn that directly into an IP address and use it. Some implementations of gethostbyname will detect the dotted format (and presumably the equivalent IPv6 format) and not do a lookup at all.

Otherwise, the name has to be resolved. And there's no guarantee that your hosts file will actually be used for that resolution (first, or at all) so localhost may become a totally different IP address.

By that I mean that, on some systems, a local hosts file can be bypassed. The host.conf file controls this on Linux (and many other Unices).

Upvotes: 183

Ryan Bigg
Ryan Bigg

Reputation: 107738

Wikipedia sums this up well:

On modern computer systems, localhost as a hostname translates to an IPv4 address in the 127.0.0.0/8 (loopback) net block, usually 127.0.0.1, or ::1 in IPv6.

The only difference is that it would be looking up in the DNS for the system what localhost resolves to. This lookup is really, really quick. For instance, to get to stackoverflow.com you typed in that to the address bar (or used a bookmarklet that pointed here). Either way, you got here through a hostname. localhost provides a similar functionality.

Upvotes: 68

d_ethier
d_ethier

Reputation: 3911

There is nothing different. One is easier to remember than the other. Generally, you define a name to associate with an IP address. You don't have to specify localhost for 127.0.0.1, you could specify any name you want.

Upvotes: -8

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