Within the last week I get "unknown host" from a few websites that I know are up, as I can use the IP address. Ping gets the same. This seems machine specific, as another computer also connected to my router has no problem accessing these sites, although the problem machine is connected by wireless and the other computer by ethernet cable. Something acts as if blocking DNS because the return of the error is almost immediate. I've tried turning off the firewall, to no effect. I can't find any log files that show any errors or blocking. I'm running pclinuxos-2007. Shorewall and mandi-ifw are the firewalls. Bind is installed and should be acting as a caching nameserver.

what if you use host or dig to directly communicate with a name server? try many around the world (search google) to really check the sort of behaviour you're seeing.

[@ ~]$ dig www.zms.org
;; Got SERVFAIL reply from 127.0.0.1, trying next server

; <<>> DiG 9.3.2 <<>> www.zms.org
;; global options: printcmd
;; connection timed out; no servers could be reached

This is what happens with all the sites in question. Other sites that have no problem return much information using dig. The resolv.conf file in this distro is an automatically written one with no information. Why is lo not working here?

so is 127.0.0.1 your dns server? you're running a local bind instance or something?

Solved: I had installed a local bind to have a caching nameserver, something I've used for years without problems. Well, this bind seems to have some problems that I can't quite figure out because it seems random and the problems didn't show up immediately, but shutting it down and also having to reboot has fixed it.