Something's up either with my ISP or with my router - or possibly with all four computers on my home network simultaneously (though that seems unlikely). Help!

Here's the problem. Although my ADSL router reports a successful modem connection and an internet connection (it has an IP address and lists a couple of DNS servers etc.), I can't do certain internet-type things. Specifically, I have noticed that I can't:

- browse the web (browser or wget reports a connection with website, but then waits for ever and nothing appears)
- browse ftp sites (I can log on to ftp sites just fine, but the ftp client stalls while trying to retrieve a directory listing)
- collect mail from POP servers (most of the time, that is; occasionally this does work)

What's mysterious is that the following internet-type things still work fine any time I've tried:

- pinging (if pinging were all there was to the internet, I'd be a happy bunny)
- traceroute (give me a host and I'll traceroute it for you!)
- getting the time from an ntp server (no problem)

In addition, there seem to be no problems on my LAN. Each computer can see the others just fine.

I've tried soft-rebooting the router, powering it off an on, running the router diagnostics, and removing firewalls - all to no avail. What's going on? Does it look as if the router's at fault, or should I be giving my ISP a call?

do standalone testing w/o router if problem same then call isp to reset your connection

I would hazard a guess that this is a problem with name resolution.
Check this by doing in a terminal;
$host www.google.com
This will list the ip address then use the ip address in the address bar of a browser. If it works then it is likely to be a name resolution problem.
Have a look at /etc/resolv.conf and see if the dns servers listed there are the same as those picked up by the modem router. Alternatively use the ip address of the router as the address in resolv.conf as most of the routers do caching.

For the record: this must have been a transient problem on the ISP end. I went on holiday the day after this problem cropped up, and upon my return 10 days later everything worked fine. (Or perhaps my router just needed a holiday too. )