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As of about 3pm PDT today, about 50% of the requests made to my webserver via the domain name have failed from various locations worldwide (as reported by my monitoring service Pingdom). The error that Pingdom reports in their logs is "No route to host". When I try to access the website myself, I am able to connect only about half the time. However when I try accessing it by its IP number, the site immediately comes up. GoDaddy provides my DNS hosting services, and I have not made any changes to the A record in months. The A record is pointing to the correct IP number. I contacted GoDaddy, but they insist it is not a DNS issue and pointed me to the website http://www.whatsmydns.net/#A/. This tool showed that my domain name quickly resolves to the correct IP from all locations. But my hosting company, which so far has been very competent in resolving issues quickly, insists it's a DNS issue. They are not experiencing any issues, and the datacenter where my server is located (it's a hostway DC) says that they are not experiencing any issues at the time. I have not touched the Apache config files recently at all.

Where else might the problem be?

Derek

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Please indicate what domain you're talking about. –  Stephane Nov 5 '10 at 7:56

3 Answers 3

I contacted GoDaddy, but they insist it is not a DNS issue

Most likely correct. Unless some of their DNS responses are answered with the wrong IP... this is not a DNS related error message.

The error that Pingdom reports in their logs is "No route to host"

Does Pingdom give the IP address it tries? If it is consistent AND CORRECT this is not a DNS issue at all.

But my hosting company, which so far has been very competent in resolving issues quickly, insists it's a DNS issue.

If the IP address tried to be contacted is correct everywhere, this can be ruled out. Once the requesting computer has the IP for the name, DNS is out of the question.

They are not experiencing any issues, and the datacenter where my server is located (it's a hostway DC) says that they are not experiencing any issues at the time.

Could be routing out odf their control.

I have not touched the Apache config files recently at all.

Also irrelevant. Apache is HTTP, not IP - basiaclly this is an error from the routing side, the request never reaches your server.

I would suggest setting up a second service (monitis) to validate the results. Plus finding out which IP addresses are tried to be reached. Maybe there is an issue at pingdom that makes them use the wrong IP sometimes.

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It sounds like some issue with routing or with DNS. Let's investigate this:

Use NSLOOKUP to query check whether one or more DNS servers for your domain resolve wrong. Use the settings querytype=NS to query only NS entries, norecurse to disable recursive querying (we will do this by hand later) and set the Nameserver to a.root-servers.net

$ nslookup
> set querytype=NS
> set norecurse
> server a.root-servers.net
> example.org

You will receive a list of Nameservers responsible for the TLD of your domain

Server:  [198.41.0.4]
Address:  198.41.0.4

org     nameserver = b2.org.afilias-nst.org
org     nameserver = b0.org.afilias-nst.org
[...]
a0.org.afilias-nst.info internet address = 199.19.56.1
[...]

Set one of the nameservers you just received as server:

> server 199.19.56.1
> example.org

You will probably be represented with the DNS Root of your Registration or Provider. If you have a nested setup of DNS Servers you might also need to repeat the last step until you get to the autorative name server for your domain.

example.org     nameserver = a.iana-servers.net
example.org     nameserver = b.iana-servers.net

The fact that you aren't experiencing a 100% loss of resolution is a hint. If it is DNS related most probably one of the Nameservers on the recursive way to your domain delivers wrong data.

With the above method you should be able to iterate through the possible nameserver paths and check whether or not they are delivering correct data. (Don't forget to set querytype=any)

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My host used pingability to run some tests, and one of the tests reported: "Error Failed getting glue records for ns19.domaincontrol.com from g.root-servers.net: SocketTimeoutException." So I changed name servers and that fixed the problem. I did this before having a chance to run your tests. Does this sound like the problem you were thinking of? –  user59273 Nov 7 '10 at 17:10

If you DNS is stable and consistent then......

It may just be a routing flap, where you home AS or destination AS is dropping routes. Try mtr and see where your packets cease to be routed correctly.

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