DNS Resolution

mpcarr · Post by **mpcarr** » Tue Mar 16, 2010 6:04 pm

For what it's worth, shopsmith apparently has registered two DNS servers with the .net global top level domain authority (the .net gtld) - internet.shopsmith.com and dns1.wrightfield.com. At times I am witnessing both of those domain servers becoming non responsive. Waiting a few minutes and they become responsive again. The shopsmith.net domain name resolves via these servers and thus when they are unresponsive, the site becomes unavailable. The shopsmith server IP address of 24.123.75.51 appears to remain active during this time. I suspect that if the local DNS servers provided by your ISP or other source has cached (i.e. made a temporary copy ) the 24.123.75.51 address things continue to work for you - the web site still works in other words for some users. If your local DNS server hasn't cached the address, it cannot get resolved through either of the two servers and the web site doesn't work for you. The issues is basically why the two shopsmith registered DNS servers are behaving intermittently.

Mike

beeg · Post by **beeg** » Tue Mar 16, 2010 6:29 pm

Yep it all made sense to me, GOOD JOB Heath.

So wood it help ME if I added 24.123.75.51 to my host file?

heathicus · Post by **heathicus** » Tue Mar 16, 2010 6:51 pm

beeg wrote:Yep it all made sense to me, GOOD JOB Heath.

So wood it help ME if I added 24.123.75.51 to my host file?

You could do that. But, if that IP address ever changed, your host file would have wrong information and you wouldn't be able to access the web site. That's why domain name resolution has mostly replaced the host file.

mickyd · Post by **mickyd** » Tue Mar 16, 2010 7:00 pm

After reading you explaination Heath, it's absolutely amazing that this process occurs so fast. It's amazing we can connect at all. Technology is great!!!

wannabewoodworker · Post by **wannabewoodworker** » Tue Mar 16, 2010 11:04 pm

heathicus wrote:How does DNS work?

As wannabewoodworker said, it is a hierarchical system. As he also said, there are DNS servers all over the world, each with different areas of responsibility. I'll try to supplement his explanation.

The best analogy for DNS resolution is looking for a phone number in a phone book. When you call someone, you don't dial their name, you dial their phone number. Likewise, when your computer "dials" Shopsmith.net, it really dial's the IP address that web site is on. But first, it has to find what that IP address is, and that is domain name resolution.

We'll use Shopsmith.net as our example. Your computer was given the IP address of your ISP's DNS server through another protocol called DHCP (Dynamic Host Configuration Protocol - when you connect to your ISP, this is how your computer receives certain network configuration information like a unique IP address, the gateway (path out to the internet), and DNS servers).

So, you type in "www.shopsmith.net" in your web browser and hit enter. Your computer looks in your configuration for the address of the DNS server. This is most likely at your ISP. It then contacts that server and asks it "where is www.shopsmith.net?" That server answers and says, "I don't know. You should ask one of the root DNS servers. There are several of them, but we'll pick 192.112.36.4. Ask it." These root servers keep track of which DNS servers are responsible for the various top level domains (.net, .com, .org, .edu, etc).

So your computer contacts that server and asks it, "Where is www.shopsmith.net?" That root server answers, "I don't know, but one of the servers for the .net domain is at 192.35.51.30. Go ask it."

So, your computer asks that server, "Hey, do you know where www.shopsmith.net" is? It answers, "Well, I don't know, but according to the registrar (the company that the domain name was purchased/registered through), the DNS servers for shopsmith.net is at dns1.wrightfield.com (70.60.40.182) and internet.shopsmith.com (24.123.75.51). Go ask one of those."

So your computer asks dns1.wrightfield.com, "Ok, so do you know where www.shopsmith.net is or are you going to keep giving me the runaround?" That server answers, "Chill dude, you've come to the right place. That web site is at 24.123.75.51. Have fun there."

So then, finally, your computer talks to 24.123.75.51 and loads the web site.

Now, sometimes one of those servers may not answer, so there is redundancy built in at every level. If dns1.wrightfield.com doesn't answer quickly enough, then your computer asks internet.shopsmith.net. But if that server doesn't answer, you're out of luck and you have to wait until one of them starts answering. The higher levels are more reliable.

Also, as wannabewoodworker said, this information is cached on your computer and at your IP's DNS server. That cache is kept for a limited amount of time before the lookup is performed again.

If you want to trace the DNS resolution and find out where any problems might be, you can use this web site:

http://www.simpledns.com/lookup-dg.aspx

(It's taken me 30 minutes to write this, with tired, whiny, crying kids climbing on me and demanding various services, and I have not done any proofreading so I hope this all made sense!)

Actually Heath JMoore was the one who described it better than I. I was going to give the whole run dwon on how DNS works but figured it would be like many of my clients when they ask me. They just say Wooooooe too much information so I tried to just give the simple explanation.

The IP address of the server is probably a static IP which means it does not change so when the DNS servers are not responding you could actually use the IP address instead and still get to the website provided it is hosted on a different server then the DNS servers. Just go to Http://24.123.75.51/forums and if the server is still up and running you should be able to browse the website.

markmay · Post by **markmay** » Tue Mar 16, 2010 11:05 pm

mpcarr wrote:For what it's worth, shopsmith apparently has registered two DNS servers with the .net global top level domain authority (the .net gtld) - internet.shopsmith.com and dns1.wrightfield.com. At times I am witnessing both of those domain servers becoming non responsive. Waiting a few minutes and they become responsive again. The shopsmith.net domain name resolves via these servers and thus when they are unresponsive, the site becomes unavailable. The shopsmith server IP address of 24.123.75.51 appears to remain active during this time. I suspect that if the local DNS servers provided by your ISP or other source has cached (i.e. made a temporary copy ) the 24.123.75.51 address things continue to work for you - the web site still works in other words for some users. If your local DNS server hasn't cached the address, it cannot get resolved through either of the two servers and the web site doesn't work for you. The issues is basically why the two shopsmith registered DNS servers are behaving intermittently.

Mike

Thanks for noticing this. Looks like we missed updating the primary dns server for shopsmith.net (and a secondary issue of why our own - internet.shopsmith.com which was intended to be the primary, is unresponsive times). That should be the missing clue to resolve (no pun intended) the whole problem.

reible · Post by **reible** » Tue Mar 16, 2010 11:24 pm

Well since this is a different thread I'll mention again some of us are not seeing this problem.

Last night I was playing with using various public DNS servers and going to some universities sites which allows checking from there site to a site of your choice... doing trace routes I found several paths that were not working.

In these cases the DNS was either not getting the correct address or some machines could not route to what was resolved. One site 24.29.165.xyz seemed to be having problems with the task. It would get to the point and time out... it would come in on vxz then try to come out on xyz and end there.

I didn't have the energy to check out site but I did run it again this evening and it is still having the same problems....

Ed

beeg · Post by **beeg** » Tue Mar 16, 2010 11:50 pm

reible wrote:One site 24.29.165.xyz seemed to be having problems with the task.
Ed

And you KNOW that's a valid in use IP address?

reible · Post by **reible** » Tue Mar 16, 2010 11:57 pm

beeg wrote:And you KNOW that's a valid in use IP address?

the last 3 digits reference any of 255 addresses, for the information I wanted that doesn't really matter so I didn't bother to note it... if you want it I can run the test again and if it is still in the path I can report back... your call.

Ed

JPG · Post by **JPG** » Tue Mar 16, 2010 11:59 pm

dusty wrote:Thank you, Paul. This is more information to maul over (keeps the gray matter pliable).

I have learned that on my end of this discussion, my ISP (QWest) maintains my IP dynamically.

[ATTACH]8194[/ATTACH]

So I guess the remaining question is how/where is "shopsmith.net" resolved to an IP address.

Whenever I am unable to reach the forum, if I do a trace using VisualRoute 2010 I find that the IP address for "shopsmith.net" cannot be found.

If I understand the screen you posted, it is your qwest modem telling you the path back to you. 3com is your ethernet adapter, its mac address, 192.168... your path to the modem.