I'm having intermittent problems today reaching various web sites, chief among which is Google. They come and go on different Macs (on the same LAN/router). It's not yet clear to me where exactly the problem is, but I tend to think it's local even though things (Network settings, DNS etc.) look OK. Just in case I'm overly critical of my setup, I wonder if anybody else has been seeing this as well.

I haven't had any problems, but if the problem affects some Web sites and not others, the first place I'd point my finger is a problem with your ISP's name servers.

There's a quick way to test that. Open the Network pref pane on one of the affected Macs. In the Name Servers filed of the TCP/IP settings, put

8.8.8.8
8.8.4.4

These are the Google Public DNS settings. If you do this and the problem vanishes on that Mac, you will have definitively identified the problem as your ISP's name servers.

Thanks, tacit. Your suggestion was one of the first things I checked; I have Earthlink as ISP and use its DNS servers, but also keep Google's and OpenDNS's server IP#s in my DNS list. As I'm still having this problem, a DNS issue seems not applicable.

As I mentioned above, the problem occurs on several Macs, but most frequently on an iMac G5 running Tiger; I haven't been able to get to Google on it for hours now. Before that Google access was intermittent, with problems frequently (but not always) reappearing when I tried to access search results. Meanwhile, an MBP running Leopard is having the same problems, but much less frequently.

I suspect some sort of issue with the wireless and ethernet configs of the Macs involved. I just cycled Airport off and back on again on the recalcitrant iMac (w/ both ethernet and wireless active), and now it can reach Google again (the MBP is usually wireless only). Let's see how things develop.

can you try ping, traceroute, and curl from terminal and maybe get some more information?

Right now Google (and other sites as far as I tried them) is still OK, and (not surprisingly) those network functions you suggest behave normally too. Unfortunately, I didn't run them while the problem manifested itself, so I cannot provide more info on that condition.

Update: things remain OK today (Sunday), but I still have no clue about the cause of yesterday's Google glitch. As if to keep me on my toes, I ran into a missing airport issue with the MBP reviving it after an overnight battery calibration, but a simple reboot eventually resolved that. Pfff...