Odd error - No internet for one computer

[Lucky75]

Hey,

I'm having a very confusing problem with my router. Someone on the network can't seem to visit any web pages, but everything I've tried and eliminated tells me he should.

- I can get an IP (which WAS static, now I removed it), and can ping the router and other computers on the network fine.

- Pinging google resolves the url so I DO get an IP, but get "destination unreachable".

- Traceroute gets through to the router, but then can't go any further.

- Its not a DNS issue because I can get an ip, and when I ping the ip of a server I still get the destination unreachable error.

- Connecting directly to the modem works, so it isn't anything to do with the NIC. That means it HAS to be the router, right? I've tried different ports on the router too, same problem.

- The computer was just formatted, and any firewalls are turned off.

- All other computers on the network work fine.


I really don't know what's wrong, since some of these symptoms contradict others. Any suggestions? Using beta5 still. Thanks!

[Eric]

Are access restrictions enabled? If so, what sort of rules do you have defined?

[Lucky75]

Nope, no restrictions.

[Eric]

You're right, that's really weird.

I don't have any ideas about what is going on, but the first thing I would check is whether there was a lot of traffic on the rest of the network causing congestion.

If that wasn't the problem I'd log in to the router via ssh and monitor the iptables rules

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iptables -t filter -L -v

Then, insert a rule at the head of the FORWARD chain that will match the IP of the problematic box:

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iptables -t filter -I FORWARD -s [ip of problematic host]

The rule doesn't do anything on match, but you can monitor byte counters on it. See if the counters increment as you try to connect from the original box by repeatedly running:

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iptables -t filter -L FORWARD -v

If the rule isn't getting hit then you know the packets aren't getting to that point in iptables before being blocked. If it is getting hit, then the problem is elsewhere.

Of course, before going to that much trouble I'd be pragmatic and see what happens if I reboot the router, especially if you're running a box with only 16MB of memory. If it runs into a memory limit weird things may start happening, though usually it just dies completely or reboots itself.

[Lucky75]

Yeah, It happens all the time now, and only on that computer. I've rebooted the router a number of times too, and sometimes it's the only one connected.

I'll try the iptables, but it will take about a week before I have access to the computer again.

Thanks for the help!

It's weird though, because it WAS working...then I think he installed skype on it and it stopped working (not sure on the timeframe here). Then he reformatted, and it still doesn't work, so skype can't have been the problem.

[Lucky75]

To follow up on this:

For the week where the lease was one IP, there was a problem. As soon as the dhcp lease expired, and the computer got a new IP, everything was fine again.

Not a big deal now, but may be a bug somewhere?

[Eric]

The default lease time is 12h... you set it to a week? Any particular reason? Also, if you tried rebooting the host machine that usually results in a new lease being given-- you didn't try that?. If it's a bug it would be in dnsmasq which is used by DDWRT, Tomato and OpenWrt (and therefore Gargoyle), and it's fairly stable.

One possibility is that there was a computer connecting with a static ip on your network that was in the range being handed out by the router's dhcp server. That would cause a conflict and could be responsible for what you observed. That would explain why a different ip would fix it.

[Lucky75]

The default lease time is 12h... you set it to a week? Any particular reason? Also, if you tried rebooting the host machine that usually results in a new lease being given-- you didn't try that?. If it's a bug it would be in dnsmasq which is used by DDWRT, Tomato and OpenWrt (and therefore Gargoyle), and it's fairly stable.

Yeah, it was set to a week. However, the computer was rebooted about 20x or so. We even reinstalled the OS thinking that it might be a problem on that end. It still didn't change IP's, even after I removed the mac address from the static IP list.

One possibility is that there was a computer connecting with a static ip on your network that was in the range being handed out by the router's dhcp server. That would cause a conflict and could be responsible for what you observed. That would explain why a different ip would fix it.

There are only about 12 computers on the network, and all of them have their own static IP's set. None of them really know how to set a static IP manually anyways, and no one else was complaining about internet problems? I guess it's possible, though it seems unlikely. Anyway, it hasn't happened again since. It'd be nice to track down what the problem was though, I'm rather curious. Everything seemed to be contradicting each other.