hantslug@??? wrote:
> Thanks, Simon.
>
> On Saturday 19 January 2008 11:47, Simon Capstick wrote:
>> hantslug@??? wrote:
> [snip]
>>> My ISP suggested firewall problems and advised uninstalling my firewall,
>>> rebooting and installing it again, so that it finds the new connection.
>>>
>>> Sadly, since I haven't yet installed a firewall on this box, I can't
>>> uninstall anything. (Unless, of course, Etch put something there. But
>>> if so, I still can't uninstall it because I don't know what/where it is.)
> [snip]
>>> Meanwhile, on my main box I can't access Firefox or aptitude update ("it"
>>> can't connect). (Tho' Konqueror works most of the time) Which also means
>>> that I can't install anything. :-(
>
>> Well you could always try a 'live' CD distribution on that PC (a distro
>> that boots from the CD and doesn't touch your hard disk). If that works
>> then you know you probably need to reinstall or find the software problem.
>
> If anything worse - on all three computers.
>
>> Otherwise if that fails try testing the PC with memtest. If that fails
>> with one or more errors then you have a hardware problem in your PC.
>> Ideally you should run memtest for 24 hours if you can, or longer if
>> intermittent problems take more than 24 hours to occur.
>
> I have only run memtest on one of the computers - but the other two work fine
> on everything else.
>
>> If that passes then the problem probably lies outside the PC, or with
>> the PC's network card.
>>
>> At which point you need to start eliminating problem areas on your
>> network. Try plugging the PC directly into the router (no intermediate
>> network switches or homeplug devices) with a known good cable. If that
>> fails then you need to look more carefully at the router and the PC's
>> network card.
>
> That fails - but on my computer everything except Firefox and the command line
> can connect OK some of the time.
>
> I have tried 4 network cards in 3 computers. And 2 routers. The only thing
> that I have been advised to do - other than those siggested by the LUG is my
> ISP's suggestion of firewall problems, which advice I have tried to follow,
> but see above. And anyway, at that rate why do Live CDs not work?
>
> :-(
> Lisi
>
Hmm, that is weird. That would seem to point the finger at the router
(config or hardware problem) or the ISP.
The only simple causes of weird network behaviour I remember having were
caused by an ip address conflict or one of the PCs or router having
different subnet masks in their network config. It's always worth
double checking your router (DHCP server settings too) and PC network
configs.
You can also check the Linux PC's firewall by looking for iptables
rules. Try using:
iptables -L
If there are no rules then there is normally no firewall running on that
PC and the output should look similar to this:
#iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Just to confirm, did you try a live CD in a Linux PC (that passed
memtest) directly connected to the router?
If yes and you still had problems then see if your router has a logging
feature, and see if it successfully connects to the internet and
receives an IP address and DNS server addresses from your ISP. See if
the same DNS servers are being used in the PC's /etc/resolv.conf. They
may use your router's IP address as their DNS server, which may or may
not be a problem depending on whether your router has DNS server
functionality.
Also see if you can enable logging in your router to monitor your
outgoing web page requests and to log any blocked traffic, i.e. log
everything!. This may show if the router is blocking specific traffic
or whether no responses are coming from the Internet/ISP, or the
requests from the PC are simply not reaching the router.
Disable any keyword or website blocking functionality in the router too
just in case.
Also check any online forums for your specific router and see what
version of the firmware you're using in case it's really out of date.
Fingers crossed you find the source of the problem (at which point it
can be fixed).
Simon
