How to combat slowness of Wifi?! "Another device is using this computer's IP address"

[mnya]

SLOW - I don't know exactly what the problem is, as the router and internet is the landlord's, who refuses to do anything about its super sluggish connectivity that started a few weeks ago when a new resident moved in and his Mac started showing up on "SHARED" in my Finder, with a constant message of "Another device is using this computer's IP address" whenever I wake my Mac from sleep (oh I get the message even when nothing is in "SHARED," though)

So can I just buy one of those Wifi extender devices - the little box like things at Walmart and set up my own network (within the landlord's Wifi(?- that's how it works, right?) and then would I be able to use Wifi faster?

Or is there another electronics I need to buy to connect faster?

The landlord doesn't give a s^!t so no calling the provider even though multiple residents have already complained and he even suspects that the new resident brought the problem (hacking the network or something..)

The router's acting up more and more each day - now I have to restart it a few times every hour to bring it up to barely acceptable speed.

One weird thing is that after restarting the router and if my Mac doesn't give the "Another device is using this computer's IP address" message, then internet is still slow so I have to restart the router again and again till I get the message...

Any ideas on what's going on? And what can I buy?

 

[FreakinEurekan]

Sounds like maybe the new user is set up with a static IP.

What I'd do in your case, is get my own router. If you have physical access to the landlord's router then a simple Ethernet cable to there on your router's WAN port would be best - if you have to connect via wifi then it gets a little trickier but still do-able.

Figure out what the landlord's DHCP range likely is (i.e. if you currently get an IP like 192.168.0.50 then his range is probably .50-.99 or so) and set your router's WAN address to a static IP in the same subnet, but as far off the range it's giving out as you can (so if it's putting out starting at .50 go below, e.g. 192.168.0.7 - or if it starts off at .2, go high like 192.168.0.251). Then your router will use its own range of say 192.168.7.x.

You'll be double-NATed which could cause issues with some services like gaming, VoIP, etc. but for 99.9% of normal Web use won't hurt anything at all.

 

[mnya]

Thanks!!!
His IP seems to be 192.168.0.100 or 192.168.0.101 depending on the time of day (?)
So should I set my router to 192.168.0.150 or something?
I'll need to connect to his router via Wifi, not its port