Can my landlord access my personal network because he controls the upstream connection?

Can my landlord access the things on my personal router's network because he controls the upstream connection? For example: the DLNA on my NAS, a public file share on my NAS, or the media server running on my laptop?

My configuration: I have my own router and connected to it are a NAS (wired) and a laptop (wireless.) The INTERNET/WAN port on my router is plugged into a LAN port on my landlord's router. The INTERNET/WAN port on my landlord's router goes to the cable modem. I am the only one with access and the password to my router. I don't have access or the password to my neighbor's router or the cable modem.

No, your router should block incoming access to your LAN just like it would if it was connected directly to the Internet. He may be able to sniff your Internet traffic though (since he's between you and the Internet).

Perhaps check out these other SU questions:

• How much information can my ISP see?
• What information can my ISP see from my router?

The other answers are basically correct, but I thought I'd expand on the topic. Hopefully this information will be useful.

As long as you have your router in a standard configuration, it should block unsolicited incoming network connection attempts, essentially acting as a blunt firewall.

Port Forwarding

Settings which increase your exposure surface would be forwarding any ports into your local area network (the devices connected to your router).

Be aware that some services on your network might open ports via UPnP (universal plug and play), so if you want to be certain that no-one is snooping inside your network, consider disabling UPnP in your router's settings. Be aware that will prevent anyone connecting to a service on your network, such as hosting a video game.

Wi-Fi

If your router has wi-fi, consider that someone can potentially connect to it. Someone who connects to your wi-fi service is essentially on your local network and can see everything.

So, if you use wi-fi, make sure you use the maximum security settings. At a minimum, set the network type to WPA2-AES, disable legacy support, set keys to reset a minimum of once per 24 hours and choose a complex wi-fi password.

Protocol Sniffing and VPNs

As your landlord sits between you and the public internet, he could potentially look at all traffic going into and out of your router. This is relatively easy to do and there are freely available network diagnostic tools to do this with.

Encrypted traffic between your browser and a website is generally safe as far as the content goes, however your landlord would be able to see what websites you visit (though not necessarily the specific pages).

However, consider that many web pages are not encrypted, and then there are all your mobile apps, email and other online activity which is potentially sent in the clear.

If you want ALL your traffic to be encrypted then you need to use an encrypted virtual private network (VPN). A VPN connects your network to the network of a VPN operator (usually a commercial enterprise), using encrypted protocol tunneling.

Ideally, the VPN would encrypt using AES encryption and the connection would be established at the router level so that all WAN traffic (to the internet) is encrypted and routed via the VPN.

If the router doesn't support VPN, then you'll need to set it up on each and every device (computer, phone, tablet, console, etc) who's traffic you want to secure.

Encryption

As a general security principle, I advocate strongly encrypting all traffic. If everything is strongly encrypted, anyone snooping on you will not know where to begin. But if you only encrypt "important stuff", then they will know exactly where to attack.

The router should stop any connections originating from outside the WAN port - Eg, if your NAS is behind the router and the router has no port forwarding on, you are safe.

That being said, if your internet traffic goes through his router then he can (assuming he has the know-how) see all the sites and traffic you visit so just keep that in mind.

Your landlord cannot access your network behind the router just like his ISP cannot access the network behind his router due to Network Address Translation. He is basically your ISP and has assigned you an IP address. All he can see is your router as long as you have it secured. You can however, see what is on his network as he is outside the security of your router. His network is secured from the ISP but is exposed to your network, while you are secured by your own router. Think of it as living in a house where you have to go through his room to get to your room. You lock your door, so he can't go into your room, but you can go through his room to get outside.