Yesterday my ISP, Comcast, had a problem in my neighborhood and I could not access certain websites, Comcast and others, they just would not load, other websites like this one loaded no problem. Also could not download or send mail, using Apple Mail, but the Email notification app worked fine telling me how many emails were on the server. Also have a clone on a separate HD so I fired that up and that exhibited the same issues.

Called Comcast tech support and they said it was a problem with my Ethernet port. That doesn't really make sense to me as it is always the same websites that will load or not load. He suggested I change my network to wireless which I did and now everything works fine. No problem loading sites or downloading email.

If it's my Ethernet port, how an I reset or check it? Did and internet speed test and it says 50mb but still certain websites will not load but will load when on wireless. How can the Ethernet port not load certain sites and load others, and not access the mail server but my Email notification app can access the server to give the correct number of emails. That just doesn't make sense to me.

Any assistance in figuring this out sincerely appreciated. Thanks. Oh and I'm using a late 2009 Mini running OS 10.6.8.

Very weird that things just spontaneously started working again. Can't help but think it was my ISP as the problem began literally within minutes of the reported ISP 'network' problems.

I did have to delete and re-input all of my email incoming and outgoing server data and mail works now too.

That sounds like a DNS (Dynamic Name Server) problem. The DNS converts URLs into the numeric IP addresses used to route internet traffic. Sometimes there is a glitch updating the name server tables which would result in exactly the situation you described. It will heal, but it may take some time for that to happen.

Public DNS servers are by and large and on the average faster and more reliable than private servers as provided by the various ISPs. There are a number of public DNS servers. You can find a list of public DNS servers here. From posts on this forum I have to believe Open DNS is the most popular and it is the one I have used and recommended for many years.

You can set the DNS server in System Preferences > Network > Advanced > DNS. The IP addresses for Open DNS are:

208.67.220.220
208.67.222.222

Do I just add those 2 open DNS servers or do I replace the ones my ISP uses?

Thanks for the info. Just didn't make sense to be the the ethernet port could make some sites load and others not.

You can do either but I chose to replace rather than add on and I have never had a problem. In fact, I edited the DNS server IP addresses in my router to use Open DNS, because that effects not only my Macs but also my iPads and iPhones when they are connected to our WiFi network.

You might also go to the Open DNS website and check out some of their other options including DNScrypt encrypted DNS access for increased internet security. Several of us have been using their beta for a long time, with good results.

Adding DNS options instead of replacing them has the advantage that you're more likely to maintain service when your primary (and possibly following) choice experiences problems, however rare a scenario the latter may be. You'll experience a small delay (which you may not even notice), depending on how long a particular name server is tried before the Network software skips to the next one on the list*. But however temporary such DNS glitches may be, a slightly increased wait (with several DNS choices) is better than no service at all (with a single but balking DNS option).
My personal multiple-redundant DNS list is topped by my ISP's DNS offerings, followed by OpenDNS and Google's public DNS. Like joemikeb I don't recall having had problems with this setup.

*) Experience plus trial and error may tell you how frequently various name servers have issues, allowing you to sequence your DNS selection accordingly, but the limited effect of this fine-tuning may not be worth your effort.

Thanks to both Joe and alternaut. Mission accomplished. This is very helpful information. Am pretty competent with mac's but know and understand little about networks.

I just looked in my network settings and the DNS address listed, and the only one listed, is for the router: 10.0.0.1. I do have a static IP address (from long, long ago…).

Would adding the above IP addresses interrupt things? Does this mean it is best to edit the DNS in the router settings?

I see that too when I look at my Airport settings in Network Prefs. My DNS selection is listed under Built-in Ethernet.

You can manually set the DNS in your computer and that will override the settings it normally gets from your router. As I said, I reset the DNS addresses in my router because that works for all the internet devices in the house including the iPads and iPhones. In that case your 10.0.0.1 DNS address is in turn routed to the Open DNS servers.