Friday, February 24, 2006

Windows XP DNS Cache problem

I never thought that famous Windows XP DNS Cache problem comes in my way. Someone told me about this problem couple of years back, but I just ignored it with the feeling that I would ever have to encounter it personally.

The problem is about DNS cache. When ever you visit a site from a browser or try to ping a hostname from command line, XP looks for “A (Host) Record” of that hostname in its DNS Cache.

DNS Cache can be accessed from command prompt using following command

C:\>ipconfig /displaydns

Here I listed typical entries. One of type CNAME and another of type A (Host) Record
Record Name . . . . . :
Record Type . . . . . : 5
Time To Live . . . . : 9015
Data Length . . . . . : 4
Section . . . . . . . : Answer
CNAME Record . . . . :
Record Name . . . . . :
Record Type . . . . . : 1
Time To Live . . . . : 4399
Data Length . . . . . : 4
Section . . . . . . . : Answer
A (Host) Record . . . :

XP has its own algorithm to add items into cache. It normally adds records based on “Time To Live” parameter or based on frequency of access. If TTL is very small it doesn’t make any sense to add it to cache even though it is frequently accessed.

The problem I faced is with expired A (Host) Record entry in DNS cache. I have a domain account with Yahoo and hosting account with znetindia. I changed nameserver settings in my yahoo domain account to point to my new name server provided by znet. I left “A (Host) Records”, CNAME Records and MX Records as they were in Yahoo. I have new entries for them at my new nameserver with znet.

When I try to access my page say with the request or sometimes it takes me to my old starter webpage with Yahoo.

I got following of solutions to get around with this problem.

check for entries in DNS cache, if there are expired entries then consider flushing DNS cache by following command

"C:\ipconfig /flushdns"

If there are no entries in DNS cache try adding an entries at the end of

“c:\WINDOWS\system32\drivers\etc\hosts” file

Try to ping your domain and check IP address. Based on that change your “A (Host) Records” and CNAME records in domain control panel

Also consider adding following two entries to registry key


Block XP from adding unresolved or failed (Negative) entries to cache

DWORD: MaxNegativeCacheTtl

Value: 0

Force XP to keep valid (Positive) entries only for specified time. This will be useful if your ISP/Domain registrar updates DNS entries more frequently than your XP DWORD:


Value: 14400

Wednesday, February 15, 2006

What is in IBM's new P6

There is a new hype about IBM's P6. Recently we were discussing about why Industrial Automation controllers are not catching up microprocessor technology updates.

So following is the update that ISA published about IBM's P6

For years, chipmakers have improved computer performance by shrinking the size of transistors, squeezing more of them into smaller spaces, and ratcheting up the speed at which they process instructions. Recently, the benefits have diminished as the chips’ power requirements and temperatures have risen.

To get around the problem, the industry has resorted to building two or more computing engines known as "cores" on a single chip and throttling back the clock speed to prevent a silicon meltdown. As a result, performance does increase, but it does not double, even with two computing cores.

IBM claims its upcoming Power6, which is multicore and designed for higher-end servers running the Unix operating system, was crafted from the ground up to run fast without major losses in power efficiency.

Power6 is expected to run somewhere between four and five gigahertz.

Can someone focus on it and post what is special with IBM's P6

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