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I think my router is blocking connections to an outside FTP server or internet printer. I can connect to my NAS on my 3G connection, different office site, but not at home. All seems set up correct with port forwarding etc... which it must be for me to be able to connect everywhere else but home. Ive tried disabling the firewall and it makes no difference. Simply says server not found. However I use a different connection then it works a charm!

Any ideas? It's an O2 II Wireless Box and the firmware is up to date.

Many routers have an issue with what they refer to as loopback. That is connecting to something inside your home network, using the external URL. If that's the case then using the IP address allows connection.

I'm no kind of Guru, but that's a problem I had with my router.

I've been using the ip address for connection as I have a static one at the one office.

Not sure I've understood your setup, but for me I have the 'internal' IP address on my private network and the 'external' one which is the one pointed to by domain servers. So if you are using the external one it amounts to the same thing as your router needs to route it external and then back.

Forgive me if I'm teaching you to suck eggs, as I know you are rather literate in these things, but it gave me some severe grief so I thought it worth explaining.

Ah gotcha on that but...

NAS is on the office network at work. All works fine on the internal IP and the router is setup for port forwarding to allow incoming connections. Set it up at work because I have a static ip address which saves bothering with something like no-ip.com

At the other office I can connect fine. I can pull the files and upload etc... This is through the external ip address

On my iPad and iPhone on the 3G I can also connect no problem using the external ip.

At home I can't do anything. Doesn't work from desktop, the iPad on wifi, laptop. Works fine on the 3G so Im assuming it's my router.

Right, I get you. Certainly sounds like a Router issue, but couldn't say what unless it's a ports issue. Some routers block most ports by default, and if the outgoing or incoming connection is one of thos blocked, but you've probably looked at that already.

Is it possible that your ISP is blocking the port?

I use O2 at all sites with only home being the issue, so I don't think so.

Could it be a firewall issue?

Disabled everything Mick, I think I have another router so will try swapping them out to determine whether it's the router.

Try using a port checking tool like this:

http://canyouseeme.org/

You might prove it's the router, but you may find that the service at the other locations is different. For example at work you have a fixed IP address which means it's not the same O2 service as at home.

Cheers Duncan I'll have a look, also got a second router at home now to link up which I'll try in a bit as well!

If one of the routers can be set up to disable NAT, then you will effectively be straight on the net, with your PC taking a direct IP from your ISP. Then it can't be anything other than the ISP (or a software firewall).

My monies on a firewall, possibly at the ISP. Disabling NAT shouldn't make a difference as the DHCP address supplied by the ISP is the only one in the equation when accessing the outside world.
Another thought. UPnP, not knowing how the software you are using is sending request. For example Apples Back to my Mac, which is basically accessing a remote machine by tunnelling IPSec over UDP requires UPnP which very often can be blocked by a firewall along the line. Not trying to confuse, just chucking in a pointer in this dark art which is networking.

NAT itself won't make any difference I agree. But if there's port blocking going on, my thought was turning off NAT would bypass it. I'm a dabbler, but it seemed like something to try.

If you are using a unix system you could try dns-sd -X udp 123 456 789
If the external port result is 0 then your routers UPnP implementation doesn't work with your system. If the external port is >0 then it is unlikely your router is the problem. This is presuming you are using UPnP.

Tell me to shut up if I'm on the wrong track please.

@Duncan, everything is worth a try, even switching something in and out can sometimes magically fix this type of issue.

Monk, how did you get on?

Last year I took out a network kit to east Africa and tried to get it work on 3G using the mobile phone laptop dongle primarily for wireless printing and internet in the house as the landlines do not work at all. I failed. It is another string to my knowledge to see how you or Duncan managed.

I swapped the router over, and it worked for a period and then stopped! Completely flummoxed!

Given you disabled firewall and the router worked for a while something has changed outside your control. If I may suggest, you could contact your server for technical support - a talk through installation/solution as it is clear that something is different from how it should behave. I hope they do not blame it on the router and refer you on.

I finally got this solved but don't understand why. I rang O2 tech support that told me they only block port 25 for reducing spam and that for sending email I simply use their relay server. I already had this setup. I asked them why I could not access my ftp server located at work on my home broadband when from the other office I could. I was asked what a ftp protocol was which was when I realised they didn't have a clue really so asked them to explain the difference between my service at home to that of work. The only difference... static ip. So after some haggling I got my monthly sub half price and a static ip which took the cost to what I'm paying now give a few pence, so quite happy. Just set up the router for static IP and it works. I can connect to the ftp server at work from home!

Now... at my girlfriends, who is on Virgin, I can't connect! How on earth do commercial enterprises with ftp servers host them so everyone can access them? Thats all id like to do, but mainly me anywhere! Not everyone has a static ip! Apparently they dont block port 25 on a static ip at O2 so would this make some sort of difference? I dont see how, but im not too clued up! They assure me this is the only blocked port on a dynamic address.