Ok ... I'm lost. An old friend of mine passed away a few months ago and I've taken over responsibility for keeping his Red Hat system running. He was an expert in this area, but the majority of my *nix knowledge (what little there is) comes from a thousand years ago (well, more like the early 80's). So I'm quite lost here just trying to figure out what all the pieces are (and are named).

The system is running (and yes, I have the root password) and booting up tells me that I'm running Red Hat v2.4.20-8 (on a slow Intel box). (I'm afraid to patch or upgrade it until I'm more confident in what I'm doing.)

In the past, he had everything running nicely, and it had several services running on it including a small web site. He also had some kind of advanced (self-adjusting, I think) security installed on it to keep out the hackers and SKs. I don't want to undo all this hard (and good) work and try to rebuild everything from scratch. For one thing, I don't have time to re-learn this entire (new-to-me) world. Even though I'm an experienced programmer and knowledgable about many other things, there's just too much knowledge to try to absorb all at once.

The specific problem that I'm having at the moment is that the web site is inaccessible, and I need to get it up and running again fairly quickly. I can get at it from inside the home network just fine, but from outside the firewall I'm getting no response at all (it just times out). From these symptoms, and the fact that it used to be running fine, it sounds to me like Apache is working properly but that some security device has automatically turned off access from the outside world. However, I can't find where it might be getting blocked in order to repair it.

I think it's important to the problem that the connection is (currently) running on a dynamic IP address, and because of that all requests are being routed through NO-IP.com. I've checked NO-IP and everything seems to be fine there (correct addresses & such). However, that means (as I understand it) that NO-IP redirects all requests in real time, so that any incoming packets probably appear to originate from NO-IP's servers. If so, then that might easily explain why a security system might have auto-blocked such an address (if hacking attempts had all been labelled with it) and then why such a blockage would then affect all other users in the world.

There is a Linksys hardware firewall in front of the box, but it also seems to be correctly configured.

I've wandered around the system a bit (quite clumsily) and made a few non-discoveries:
* iptables has no rules
* ip6tables says it can't find the 'filter' table
* ipchains complains about being incompatible and refuses to run

So, my guess is that my next step is to figure out what is blocking external requests. (From there I can then research enough to figure out how to change it.) So, unless someone has a better idea or something else to try, here's the big question:

What can I do to figure out what security system is (auto-)blocking incoming packets?

TIA for any help I can get!

I can't answer much but I'll take a stab at it.

For allowing the system to be seen from the outside world....

In the router check to see that port 80 forwarding is enabled for http requests to the local IP that the server is at.

Yes, it is. Any other ideas?

One thing I have found, sometimes No-Ip will get the IP wrong. So you may want to login to no-ip and check that the IP listed there and the one you see in your router statistics page match.

If that fails try the following commands

killall no-ip
killall apache
apache
no-ip

This will have the effect of stopping No-IP and apache and starting them again, amazingly it actually works quite well.

Keep me posted on progress

Shane

I've done that, and they match exactly.
I can certainly give that a try. But I've rebooted the whole system a number of times -- are you expecting this to do something that rebooting hasn't already accomplished?

I guess another couple of steps to check are:

Can you access the server from outside of the network using the external ip address rather than the website name?

Are there any entries in /etc/hosts.deny /etc/hosts.allow that might affect it ?

Apache isn't listening on 127.0.0.1 is it? (Guess it isn't though as you wouldn't be able to access it from inside the network from another computer)

AHA! Found it!

It WAS NO-IP, after all. It turns out that what I thought they said they were routing to wasn't the routing address at all. So I've obviously got a failure to keep their system updated, and I can figure out how to deal with that, now that I know what to look for.

Thanks much for all your help!!!

(My next problem will be doing a trick with virtual hosting, splitting one incoming address+port into two machines based on host name. I'm hoping to deduce the right settings from the Apache docs.)

There are other virtual hosts out there you can use other than No-Ip, just google for virtual hosts

Thanks. I'll keep that in mind. But if things progress well enough, I'll be considering switching to a static IP for simplicity.