Hack 44 Tweak DNS Settings for Faster Internet Access
 
A handful of DNS hacks for speeding up access
to web sites.
You use the Web by
typing in hostnames such as www.oreilly.com, but web servers and Internet
routers can't understand plain English words, so
they need those letters translated into numeric
IP addresses. Whenever you type in a
hostname, such as www.oreilly.com, it needs to be resolved to
its IP address, such as 208.201.239.37. DNS servers provide that name
resolution automatically and behind the scenes as you surf the Web.
There are several ways you can hack your DNS settings so that you can
get faster web access.
5.4.1 Speed Up Web Access with a HOSTS File
It takes time to send your request to a
DNS server, have the server look up the proper IP address to resolve the name, and then
send the IP address back to your PC. You can eliminate that delay by
creating or editing a local
HOSTS file on your own PC that contains
hostnames and their corresponding IP addresses. When you create one,
XP will first look into the HOSTS file to see if
there's an entry for the hostname, and, if it finds
it, it will resolve the address itself. That way, you
won't have to go out to a DNS server and wait for
the response before visiting a web site. The
HOSTS file is a plain text file you can create
or edit with a text editor like Notepad.
You'll find an existing
HOSTS file in
C:\System32\Drivers\Etc\HOSTS. The file has no
extension; it is named only HOSTS. Open it in
Notepad and enter the IP addresses and hostnames of your commonly
visited web sites, like this: 208.201.239.37 oreilly.com
216.92131.107 simtel.net
Each entry in the file should be on one line. The IP address should
be in the first column, and the corresponding hostname in the next
column. At least one space should separate the two columns. You can
add comments to the file by preceding the
line with a #, in which case the entire line
will be ignored by the file, or by putting a #
after the hostname, in which case only the comment after will be
ignored. You might want to comment on individual entriesfor
example: 130.94.155.164 gralla.com #still in beta
When you're finished editing the file, save it to
its existing location.  |
Make sure to
check your HOSTS file regularly and keep it up
to date, or else you may deny yourself access to certain web sites.
For example, if the http://www.gralla.com
web site were to change its IP address, but your
HOSTS file kept the old, incorrect address, your
browser would not be able to find the site, because it would be given
the wrong addressing information. |
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5.4.2 Adjust XP's DNS Cache Settings
As a way of speeding up DNS,
when you visit a site, XP puts the DNS information into a local DNS
cache on your PC. So, when you want to go to a site, XP first looks
in its local DNS cache, called the resolve
cache, to see whether the DNS information is
contained there. That way, if it finds the information locally, it
doesn't have to query a remote DNS server to find IP
information. The cache is made up of recently queried names and
entries taken from your HOSTS file.
The cache contains both
negative and positive entries.
Positive entries are those in which the DNS
lookup succeeded, and you were able to connect to the web site. When
XP looks in the cache, if it finds a positive entry, it immediately
uses that DNS information and sends you to the requested web site. Negative entries are those in which no match
was found, and you end up getting a "Cannot find
server or DNS Error" in your browser. Similarly,
when XP looks in the cache and finds a negative entry, it gives you
the error message without bothering to go out to the site. Negative entries can lead to problems. When you try to make a
connection to a site that has a negative entry in your cache,
you'll get an error message, even if the
site's problems have been resolved and
it's now reachable. You can solve this problem, though, using a Registry hack. By
default, XP caches negative entries for five minutes. After five
minutes, they're cleared from your cache. But if
you'd like, you can force XP not to cache these
negative entries, so that you'll never run into this
problem. Run the Registry Editor [Hack #68] and go to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters.
Create a new DWORD value with the name
NegativeCacheTime and give it a value of
0. (The value may already exist. If it does, edit
its value to 0.) The DWORD
determines how much time, in seconds, to keep negative entries in the
DNS cache. If you like, you can have the entries stay alive for one
second by giving it a value of 1. After you're done editing, exit the Registry. To
make the change take effect, restart your computer, or
flush your cache by issuing the command
ipconfig /flushdns at a
command prompt.  |
For more information about using ipconfig, see
[Hack #52]. |
|
That command will flush your DNS cacheall the entries, both
positive and negative, will be flushed, and it will be empty until
you start visiting web sites. Negative entries, however, will not be
added to the cache if you've given the
DWORD a value of 0. You can also use the Registry to control the amount of time that
positive entries are kept in the DNS cache. By default, they are kept
for 24 hours. To change the default, go to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters
again and create a DWORD value called
MaxCacheEntryTtlLimit. (If it's
already present, just edit the value.) For the value, enter the
amount of time you want the entry to remain, in seconds, making sure
to use Decimal as the base.
5.4.3 Fix DNS Problems
Sometimes when you
can't connect to a web site, the cause
is a DNS problem. There are things you can do to solve these
problems, though. If you're having trouble
connecting, to find out if DNS is a potential culprit first ping
[Hack #52] the site to
which you can't connect, by issuing the
ping command like this at
the command prompt or Run box, like this:
ping www.zdnet.com
If the site is live, you'll get an answer like this: Pinging www.zdnet.com [206.16.6.252] with 32 bytes of data:
Reply from 206.16.6.252: bytes=32 time=119ms TTL=242
Reply from 206.16.6.252: bytes=32 time=79ms TTL=242
Reply from 206.16.6.252: bytes=32 time=80ms TTL=242
Reply from 206.16.6.252: bytes=32 time=101ms TTL=242
Ping statistics for 206.16.6.252:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 79ms, Maximum = 119ms, Average = 94ms
If it's not, you'll get a response
like this: Ping request could not find host. Please check the name and try again.
If you ping a site and it's live, but you
can't connect to it with your browser, a DNS problem
might be the reason. If you suspect you're having a
DNS problem, take the following actions: Check your HOSTS file. If your HOSTS file contains an incorrect or
outdated listing, you won't be able to connect. Even
if you don't recall adding listings to a
HOSTS file, it still may contain listings,
because some Internet accelerator utilities edit them without telling
you. Open your HOSTS file with Notepad and see
if the site you can't connect to is listed there. If
it is, delete the entry, and you should be able to connect. Check your DNS settings. Make sure your DNS settings are correct for your ISP or network. Find
out from your ISP or network administrator what yours are supposed to
be. Then, to find out your current DNS settings, double-click on the
problem connection in the Network Connections folder, choose Support
 Details, look at the bottom of the tab to find your DNS
servers. If they don't match what
they're supposed to be, right-click on the problem
connection and choose Properties. Then, highlight Internet Protocol
(TCP/IP) and choose Properties. Change the DNS servers to the proper
ones, or choose "Obtain DNS server address
automatically" if your ISP or network administrator
tells you to. Flush your DNS cache. The problem may be related to your DNS cache,
so flush it out. To flush the cache, type ipconfig
/flushdns at a command prompt. Find out if your ISP is having DNS problems. The cause may be your ISP. One possibility is that one of its DNS
servers is down, and you're trying to access the
down server. Ping each of your ISP's DNS servers
and, if any of them don't respond, remove them from
your DNS list, as outlined earlier in this hack.
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