Poor NAT loopback operation on Hub One

[#1]

I thought I'd post about this given the almost equal amount of frustration and relief the issue and resolution has given me...

For several months now I've been having issues accessing both a locally-hosted Roundcube webmail installation and some locally-hosted IP cameras. The issues are best described as occasional (sporadic and seemingly random) lack of responsiveness.

Over time I happened to notice that the issues would only manifest themselves if accessing these services locally (i.e. from the LAN) and things were perfectly fine if accessed remotely (i.e. from a mobile over a 3G connection). I also discovered that if I used my server's local RFC1918 address and not the public WAN address derived from a DNS lookup then again I wouldn't have any problems.

Given these symptoms the finger of blame started to point at the router (a Hub One) but not with all that much confidence given that its NAT loopback function was obviously working to a point, but seemingly not quite perfectly. I then put two and two together and realised that for years these services had worked without issue so what had changed? Well, my router for a start towards the end of last year.

I borrowed a friend's spare router - a BT Home Hub 5 - which didn't solve the problem... But then it dawned on me that it wasn't the best of tests given that they are essentially the same device and so I dug out an old TG582n and Openreach modem and the problems went away!

I've got a Fritz!box 7530 in the post so if that works fine I'll know for certain that whilst the Home Hub 5 / Hub One support NAT loopback, they don't do so particularly well in some cases - and these problem cases possibly being ones that involve a high number of simultaneous connections (I've got a dozen or so cameras, some of which are old and require individual JPEG snapshot requests every second). Simpler scenarios e.g. standard HTTP services, SSH etc seem to work perfectly fine.

[#2]

Interesting, but not something I can say I've experienced perosnally.

I have a good bunch of servers exposed to the Internet behind a reverse proxy, all of which are accessed using a FQDN. I'm not using a Hub One at the moment, but in the past when I have, I've never had issues accessing the services by domain name whilst on the LAN

Not discounting your observations of course, its' just something I'd expect to have experienced if there was a fundamental flaw somewhere.

[#3]

I hear what you're saying Bob, and I must admit that from all my searching I have yet to find anyone else talking about similar issues. That said, it is a tricky scenario to describe and search for  given the fairly non-specific keywords available to use such as 'NAT loopback', 'port forwarding', 'LAN', 'WAN' etc which as you can probably imagine no matter how you put them together in a web search you end up in with a million forum threads about general port forwarding issues where things are usually binary and either work or they don't. My situation is unfortunately somewhere in between.

Certainly for fairly 'conventional'(?) services such as a simple web server, SSH service or indeed anything that is perhaps deliverable over a limited number of connections everything is working fine whether accessed from the LAN or the WAN. If there's anything I can find in common with the services I am having issues it is that they all appear to use large numbers of simultaneous connections - TinyCamMonitor is accessing a dozen or so cameras simultaneously (and some of them are serving up multiple JPEGs a second to create a kind of pseudo stream rather than just a single RTSP stream, for example, and so is relatively network intensive) and Roundcube and Zoneminder are fairly dynamic AJAX-based platforms that seem to require multiple simultaneous connections to build - and maintain - an interactive web page.

All said and done I haven't been able to put my finger on exactly what my issue was, but I am able to repeat it at-will with both my Hub One and HH5 for what it's worth. With a TG582n, or indeed a Fritz!Box 7530 which I bought today (what a great modem/router that seems to be if the amount of functions and configuration is anything to go by), I don't have any issues whatsoever despite the general configuration applied being essentially being the same.

Hopefully if someone else bumps into this thread due to facing similar issues it might give then a steer to try another (different) router to see if it goes away as this wasn't something I was necessarily expecting to work even though in hindsight I think the signs might've been there (eg. only LAN access via the WAN address being an issue; LAN-to-LAN and WAN-to-LAN being no problem). Even better if no one else suffers the same problem at all as I am satisfied I've solved it for me even if I might've been blaming the wrong cause (e.g. it could be something to do with the rest of my setup - eg the server itself - and it just so happens that the Hub One / HH5 happens to bring it out through no fault of their own).

[#4]

Yep, agree it was worth posting your account.

Not something I think it's worth investing too much time getting to the bottom of though in the absence of other reports.

FWIW, I have two Roundcube installations on my local network.

[#5]

Agree it's not worthy of further investigation, and to be honest I'm not sure what additional diagnoatics could be performed.
Incidentally, the Roundcube issues only occurred with Chrome and not Firefox. This might suggest a Chrome issue but from what I can gather they do differ in how they handle simultaneous TCP sessions - not a matter of right or wrong, just different.