Own up, who broke it?

[karvala]

Ho hum, well I was merrily browsing about an hour ago, when things just decided to stop working.  Obviously, I did the usual trouble-shooting steps, which did not fix the problem but seem to fairly convincingly demonstrate that it's not at my end.  A summary of the facts:-

(1) Nothing at all changed at my end between browsing working fine, and then suddenly no longer working.
(2) I do have sync.
(3) I do have a PPP layer connection.
(4) I can resolve IP addresses without a problem (and the browsing problem occurs whether IP addresses or domain names are used, so it's not a DNS problem).
(5) I can send and receive ICMP packets, so it's not a simple routing problem.
(6) Packets can be sent to remote port 80, but nothing is received back.  Some other ports appear to be working.
(6) Using the BT test login, I CAN access their test website (on default port 80), so there is nothing inherently blocking port 80 on my machine.
(7) Switching firewalls on and off makes no difference.
(8) All settings (MTU etc.) are correct and as they were when things were working.
(9) I can VPN tunnel, and browse websites using my work connection through this same machine and router here, which again emphasises that there is nothing inherently wrong at my end.

In short, my computer and router are fine in every respect, nothing's changed at my end since it was working, and the problem is specific to the IDNet connection.  In other words, it ain't my problem!    There is a thunderstorm in the area, in case anyone thinks that's significant (though it would be curious for a thunderstorm to be selective about which remote ports it knocks out).

Anyone else experiencing this (appeared at start around 1.45am)?

[Rolacka]

It's all fine here for me , just started browsing 10 mins ago 3 am approx after the movie ended but haven't run into any problems on any of the sites I've been to.

[maxping]

Jeez 3 a.m, hit the off button  get some sleep and worry about it in the morning

[karvala]

I did, but it's now the morning and it ain't fixed. 

Same problem still.  Some amendments and additions to my preliminary information:-

(1) The VPN solution doesn't entirely work either.  It loads most sites that I've tried, but not always completely.  For example, it will load this site fine, but if I go to the IDNet homepage it will sometimes hang loading the IDnet image.
(2) Occasionally, and again consistently, on the IDNet connection, it will get a little data back on the http port, but always the same amount on the same sites, and never enough to load the site.  Most sites return no bytes at all.  On the basis of these two, it doesn't look necessarily port-specifc as I originally thought, so much as simply that things like ICMP packets are handled differently by routers and are much smaller.
(3) Tried different cables and filters, and tried with both router and USB modem (and factory reset both as well), and made absolutely no difference, so it's not an equipment ot network settings issue.
(4) Often, the router takes several attempts to successfully authenticate according to the log.
(5) Twice in the log the d/s and u/s SNR values had dropped considerably to around 5dB and 6dB respectively.  Most of the time, however, it shows the typical values of around 14dB and 16dB, which are unchanged from usual.  It's not clear, therefore, that's it a noise issue.
(6) Dial-up (PAYG Virgin) works fine.

I'm completely a loss on this; it doesn't look good.  It clearly isn't going away without aytion from someone, and I've done all I can, but getting someone to diagnose exactly what the problem is, or getting BT for example to look it when the problem isn't with obtaining sync, is not going to be easy I suspect.  As it stands, the connection is useless and I'll have to do stuff on dialup, but I can't sustain that for very long.

[karvala]

Brief update in case anyone's interested: the problem remains present, unfortunately, and Simon will raise a fault with BT tomorrow about it, although we're not quite certain exactly where the fault lies.  Discussions with Simon and further troubleshooting reveal the problem is apparently a size-related packet loss problem, which is why normally small packets such as pings get through fine, but maximum size packets belonging to any data stream, including from a website, always fail.  Reducing the MTU to absurdly low values allows most, but not all, packets to get through, but a painfully slow speed (think bad dial-up).  As to why the packet loss should have occurred, why it's worse for large packet sizes, and why it doesn't show up anywhere on the line stats (line tests show the line as clear, and the noise margins are pretty much as they were), is anyone's guess.  Answers on a postcard...