I must admit, I think it is upstream of the router. The local network is unaffected by this everything continues OK on my side of the router. Also, I never seem to wake up in the morning to find the problem. (router on 24 hrs) It seems always to be triggered during random browsing. (Oh and now I think about it, it seems to be the Linux machine that is doing the browsing at the time DNS is lost - but this is probably coincidental as this is the one that gets by far the heaviest use. ) But I don't think this machine is the cause, it has had a clean install recently. And just to stress - it occurs simultaneously to all machines. Any existing connection on any machine at the time (eg youtube stream or a download in progress) is not broken and continues unaffected, it is only new lookups that fail. Therefore, I think that the connection is good.
It doesn't seem to drop DNS unless a DNS server request is made. If the router is OK when you stop, even if it is days later, it will be OK when you return. It seems to be making DNS requests that trigger the problem. It also seems to happen mostly between tea-time and bed-time GMT. All the networked machines are set to DNS from DHCP.
I'm waiting for it to happen today so I can try a ping first.
I'm right out in the country, so line quality could well be suspect. But I'm puzzled that it only loses DNS and the connection itself doesn't drop?
BTW the router is a D-Link G604-T (and the spare is the same) I might try to lay my hands on a newer model and give that a shot.
Cheers
Last edited by Cheerio; 14th May 2011 at 08:45.