Are there any downsides to enabling guest WiFi account on my router?

Question

While reading articles regarding improving WiFi security, I saw quite a few of them recommend starting Guest WiFi networks.

For instance, see point 4 in the following article:
https://www.techradar.com/news/networking/wi-fi/five-tips-for-a-secure-wireless-network-1161225

One of the commonly cited benefits is that enabling Guest WiFi limits the number of people having access to your regular network. The idea being, only the members of the household will use the regular network and the guests will be isolated to the guest network.

Are there any downsides to this approach? Are there any overlaps between the Guest network and the regular network that an ordinary user should be aware of?

My concern stems from my general lack of education on this matter. To me it seems like creating two doors to the same house. Now I have to worry about securing an additional door, and I haven't properly understood the benefit of having added an extra door.

Edit01:
From the first two answers, I have understood that I should be thinking about the arrangement not as two doors to the same house but as two separate rooms (1 for the regulars and 1 for the guests). In this case is it typical for the router to create two separate 192.168.x.x ranges? Say for example, can the router serve 192.168.0.123 twice (since the two networks are somewhat isolated)?

Answer 1

Network segregation is an important concept on any network. There is a degree of implied trust when multiple devices are allowed to communicate on the same link. Devices on the same network may be able to probe each other and exploit any discovered weaknesses, or reroute traffic to perform a man-in-the-middle attack. Also with wireless networks, typically anyone who knows the PSK can passively decrypt all traffic.

These are just a few of the reasons why it makes sense to create a separate guest network, where untrusted devices will have no impact and gain no access to your personal network.

The problem is, I do not believe there is any official specification for how "guest WiFi" should be implemented in consumer products. So when you say your router supports "guest WiFi", I can only hope that it is implemented correctly/safely. But if it is indeed implemented properly, there shouldn't be anything to worry about; guests will be kept away from your main network, and will still be required to get a PSK from you before connecting. You would still want to keep the PSK fairly secret or have it rotate if possible so that your internet isn't used by unknown parties for illegal purposes if the key gets shared.

So I wouldn't describe it as a second door to the same house. As long as the router vendor is competent, it's more like building a guest house next to your real house, where the keys to the guest house do not work on the main house. In fact, I would even recommend creating an additional network for any smart/IoT devices that need to be connected, since they may be poorly secured.

Answer 2

To your question regarding house: It is not about doors, it about what rooms can guests access. If you have a more or less big house, then you have a separate WC, bath and bedroom for your guests, you don't want that you guests use your private WC, bath, your own bedroom, and may be you don't want that your guests visit every room in your house.

The main goal of the separating guest WLAN is to reduce the risks of unauthorized access to your private resources. Here are some examples of such resources:

1. You have one or more SAN disks in your home network where you store your private pictures and videos. May be you don't want your guests to access them.
2. You have some other sensitive data like your private financial data, political texts or videos, etc., and you want prevent access to them.
3. You have some IOT devices in your home network. You want to prevent your guests from accessing your IOT devices and taking control on them.
4. You want to make sure that no malware will access your network that can potentially attack PCs, laptops, tablets, smartphones, IOT devices in your home network.

If you don't have sensitive data in you home network, if you don't have devices that you want to protect from malware, then of course there is not much sense in having a separate guest WLAN. Otherwise it may well make sense to have it.