I do separate the router, switch and firewall topic because I assume that a lot of companies started as one man show without a business contract subscription to an ISP. So what do they get? Consumer products? Cheap modems with minimalistic security requirements?
This setup describes a company started 30 years ago without internet and the most powerfull internet available in the late 90's. 3 people sitting in the office without any time to surf for fun, because they have much better todo. The time I came in there has been already a business contract subscription - lucky me. It took 20 min on hotline to open 1 port. So time matters - one call and all ports open and router was just naked device serving a public ip range for firewall.
This router provided a synchronous 8 Mbit connection to ISP - !!WOW!! - over 15 years. No soft- or hardware upgrade over this period. That's what this part of this homepage is for! Ask your friend or admin if you could see the construction of the connection coming in from ISP - turn the modem upside down and read the manufacture sticker.
Having the software version, model number and manufacture company of your home router can give you best information how to hack your device and get root access for example. Even better - what if you check this website and calculate WLAN password of your "SpeedTouch" router?
But I do prefer the hardware hack.
- take a network cable
- put both ends in the routers switch
If it is a managed router / switch - with STP on - all is good but I don't think so because Spanning Tree Protocol is not default.
Getting access to an outdated old modem/router is not a big task. But if you have physical access to the device the job is even easier. Think about locking it in a safe room!