Port-scanning on Cisco router with Nmap

I have Cisco 2911 router just booted with factory settings and no ACLs or NAT configured. All I did is turned on the interfaces and assigned IPs.
I am trying to scan for open ports with Nmap, but the output shows that all ports are closed.
So I used

nmap 192.168.2.1

that returns

All 1000 scanned ports on 192.168.2.1 are closed

Scanning port 80 alone also shows that it is closed

nmap -p 80 192.168.2.1
PORT STATE SERVICE
80/tcp closed http

And if I try this

nmap -sT -p 80 -Pn 192.168.2.1

it returns

Host is up.
PORT STATE SERVICE
80/tcp filtered http

I also have webserver running behind the router and I can access it through browser, so obviously at least port 80 is not closed. But it is supposed to be all open, since by default Cisco router has it all ports open. Do I get some fundamental concept wrong or what can be the problem?

You are nmapping the cisco router, so you are checking the open cisco ports, not the open webserver ports behind it.

If you nmap the webserver you'll find port 80 open.