{"id":958,"date":"2021-09-22T12:42:20","date_gmt":"2021-09-22T12:42:20","guid":{"rendered":"https:\/\/www.practicallynetworked.com\/?page_id=958"},"modified":"2021-10-05T16:59:21","modified_gmt":"2021-10-05T16:59:21","slug":"power-of-the-hosts-file","status":"publish","type":"post","link":"https:\/\/www.practicallynetworked.com\/power-of-the-hosts-file\/","title":{"rendered":"Networking Notes: The Power of the Hosts File"},"content":{"rendered":"

Need to contact another computer on the Internet? You usually rely on a DNS server to look up the host’s IP address. but the system has a few issues that make it occasionally frustrating. Here’s how you can use hosts files for immediate access.<\/b><\/p>\n

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Considering the Hosts File<\/h3>\n

Have you ever registered a new Web domain, been eager to set up a new Web server, and found that you’re stuck until the new domain name registers with all the\u00a0DNS<\/a>\u00a0servers? Ever wished you could give a machine on your network a name besides its\u00a0IP address<\/a>\u00a0without having to maintain your own local DNS server? You might want to consider the hosts file.<\/p>\n

When we need to contact another computer on the Internet, we usually rely on a DNS server to look up the host’s IP address. DNS has worked pretty well for decades, but the system has a few issues, as I noted above, that make it occasionally frustrating. Those delays and lags can have some unfortunate side effects.<\/p>\n

Consider, for instance, managing systems you don’t have physical access to. If you bring up a new domain but your own\u00a0ISP<\/a>‘s name servers don’t know about it yet, you’re effectively locked out of your new server until your ISP’s DNS servers\u00a0do<\/em>\u00a0figure it out and start answering DNS requests correctly. That’s no good if you’re hoping to have something more than a “this site coming soon” splash page greeting your first visitors, or if you need to move files onto the new server.<\/p>\n

Here’s another scenario:<\/p>\n

If you’ve ever moved a network service from one host to another you’ve had to deal with a lag \u2014 though not as long as registering a new domain \u2014 as name servers register the change. That can result in two different hosts responding to requests, depending on whether the requester’s DNS server has caught wind of the change yet.<\/p>\n

Those are both instances where the hosts file can help you out by making sure your computer is pointed to the correct host in the interim between making a change to your domain or registering a new one.<\/p>\n

In a nutshell, even though computers generally depend on DNS servers for address lookups, operating systems offer an override in the form of the hosts file. You can specify the IP address for a given host name in your computer’s hosts file, and that address overrides any information coming back (or failing to come back) from a DNS server.<\/p>\n

The hosts file is located in a few different places depending on your operating system. On most Unix and Linux systems — including Mac OS X \u2014 you’ll find it in the \/etc directory. On Windows systems, it varies:<\/p>\n\n\n\n\n\n\n
Windows Version<\/th>\nLocation<\/th>\n<\/tr>\n
Windows 95\/98\/ME<\/td>\nc:\\windows\\hosts<\/tt><\/td>\n<\/tr>\n
NT\/2000\/XP Pro\/Server 2003\/Vista<\/td>\nc:\\winnt\\system32\\drivers\\etc\\hosts<\/tt><\/td>\n<\/tr>\n
Windows XP Home<\/td>\nc:\\windows\\system32\\drivers\\etc\\hosts<\/tt><\/td>\n<\/tr>\n<\/tbody>\n
Locations of the hosts file in Windows operating systems<\/caption>\n<\/table>\n

In each case, the format of the file is the same. Here’s a sample:<\/p>\n

# My Sample Hosts File\r\n192.168.1.3 ghola # local Samba server\r\n63.146.109.227  practicallynetworked.com www.practicallynetworked.com pracnet.com\r\n<\/pre>\n
The first line, which leads with a hash — # — character, is a comment. A hash character causes the computer to stop reading a given line.<\/p>\n
The second line shows a way to name a machine on a local subnet. In this case, if you try to use any network service with “ghola,” your computer will know that you’re talking about the machine at the IP address 192.168.1.3. You also see another way to use the comment character: To insert a note at the end of a line. In this case, we’re just reminding our selves that ghola is our Samba server.<\/p>\n
The third line shows one more way to make an entry, by providing an IP address, a hostname, and an alternate hostname. Note that if you’re dealing with a domain that has a number of subdomains you’ll need to include subdomains like “www,” “ftp” or “dev,” for instance. The hosts file is pretty literal in that regard, because “www.somedomain.com” could easily be on a different IP address from “dev.somedomain.com” or plain old “somedomain.com.”<\/p>\n
Earlier, I outlined two ways you could use a modified hosts file when you bring up a new host or when you move services between hosts at different IP addresses. There are at least two other scenarios where a modified hosts file might come in handy:<\/p>\n