OK.. I am surprised your Uni is handing out public IP addresses to all and sundry.
To allow a single DHCP address to work when DHCP and NAT are clearly working is a bit difficult to fathom.
Maybe I am due for a reset of my TimeCapsule? I am hesitant to do that since I am not sure what impact that house on the encrypted backup data I have stored on it.
I suspect your TC is actually faulty. It is just that symptoms are very unusual.
Lets just say your Gen4 TC time is up and it is well and truly time to replace. So figure you are going to lose the backup no matter what happens here.. if you want it and it is important.. archive it today.. now.. to a USB disk plugged into the TC.. Mac formatted. 2TB if that is the size of the hard disk .. or larger, Unless your actual data is less than 1TB in which case the smaller drive will work. You will have no choice but to start a new backup on a new device anyway.. so this is just going to be emergency fill in.
Factory reset the TC. No files on the hard disk are touched.
But do this right. Hold in reset and power on the TC still holding in reset for about 10sec until the front LED flashes rapidly.
Open the airport utility and run through the setup wizard. Give the TC a new name. Short, no spaces and pure alphanumerics.. NOT APPLE RECOMMENDED NAME.. as you have now. Your network name is fine.
Keep the TC on the default IP, ie 10.0.1.1 even if that messes up your fixed IP.. sorry but some things are just best left to their defaults.
In Time Machine you can swap hard disk destination.. TM does not check the disk until it begins the backup but it will find the existing backup and continue as long as you give it the correct encryption password.
What I predict will happen next.
I think your TC will work ok.. If it does fail immediately that is a good thing.. The actual replacement choice is then clear.
But I think the TC will fail again within a short time.. a day or a week.. maybe even a bit longer but it will fail.
Apple no longer make Airport routers but stock of Time Capsules are still available in some places. They are selling off the reminder of the stock at full price note.. and a new TC might give you a few more years before you need to rethink the setup.
If you want to look at alternative routers that support Time Machine.. Asus high end models or the Synology RT2600 do support a USB3 hard disk formatted to Mac OS. I have now done extensive testing on the Asus.. and it almost works!!!! Most testing will show it works fine.. I found it actually fails about every 8 weeks.. I have not as yet done long term testing on the Synology.
A Synology NAS is something several of us here have tested and has proven reliable long term. It is a big price jump though and you still need a router.
Post back for more details of alternatives.
Now if you are the DIYer type.
A gen4 TC had a soldering issue.. the board can be oven baked to reflow the solder.
(If it was me .. I would do this as a matter of course. Not even worry about the factory reset because I think this is more likely the problem.)
Gen4 A1409 issues - LaPastenague
This has exceeded my expectations. It reliably fixes the problem. (Assuming you do it right!!).
For your particular issue.. there is an earlier fault that was a hang over from the Gen3 TC.. see this page.
New issue with A1355 Gen 3 TC - LaPastenague
It is the second problem.. bad or unreliable TC.
The capacitors on the 1.8v line give out.. it was never a common fault.. they went short circuit rather than open most of the time.. but early model Gen4 share the board with the Gen3 .. and I have seen a couple of them with the fault. Soldering a large capacitor across the 1.8v line fixes it..
Only the first batch of TC from 2011 will have this particular problem.. never seen it on ones from 2012-13 when they went to Gen5.
I think for the DIYer these can give you a decent extension of lifespan. But for most people .. wipe the hard disk and sell it on ebay with warning that it is failing.. at least someone will buy it who is DIYer and it doesn't just go to ewaste.
BTW there is an inbetween solution.. buy a new non-apple router.. would still go high end Asus or Synology though.. but plug the TC into the router by ethernet and use it as a dumb shared network target. Taking away routing problem it might work for another year or two.. or might fail tomorrow..?? It puts off the day of decision.. that is all.
