I want to check a particular website from various locations. For example, I see a site example.com from the US and it works fine. The colleague in Europe says he cannot see the site (gets a dns eror).
Is there any way I can check that for my self instead of asking him every time?
DNS info is cached at many places. If you have a server in Europe you may want to try to proxy through it
The only thing that springs to mind for this is to use a proxy server based in Europe. Either have your colleague set one up [if possible] or find a free proxy. A quick Google search came up with http://www.anonymousinet.com/ as the top result.
Well, DNS should be the same worldwide, wouldn't it? Of course it can take up to a day or so until your new DNS record is propagated around the world. So either something is wrong on your colleague's end or the DNS record still takes some time...
I usually use online DNS lookup tools for that, e.g. http://network-tools.com/
It can check your HTTP header as well. Only a proxy located in Europe would be better.
It depends on wether the locatoin is detected by different DNS resolution from different locations, or by IP address that you are browsing from.
If its by DNS, you could just modify your hosts file to point at the server used in europe. Get your friend to ping the address, to see if its different from the one yours resolves to.
To browse from a different IP address:
You can rent a VPS server. You can use putty / SSH to act as a proxy. I use this from time to time to brows from the US using a VPS server I rent in the US.
Having an account on a remote host may or may not be enough. Sadly, my dreamhost account, even though I have ssh access, does not allow proxying.
Besides using multiple proxies or proxy-networks, you might want to try the planet-lab. (And probably there are other similar institutions around).
The social solution would be to post a question on some board that you are searching for volunteers that proxy your requests. (They only have to allow for one destination in their proxy config thus the danger of becoming spam-whores is relatively low.) You should prepare credentials that ensure your partners of the authenticity of the claim that the destination is indeed your computer.
Sometimes a website doesn't work on my PC and I want to know if it's the website or a problem local to me(e.g. my ISP, my router, etc).
The simplest way to check a website and avoid using your local network resources(and thus avoid any problems caused by them) is using a web proxy such as Proxy.org.