How do you set up a separate guest Wi-Fi network for office visitors?

In short

Enable the router's guest network with its own password and isolation from the internal network, then test it from a phone.

Why shouldn't visitors use the office Wi-Fi?

If clients, suppliers or consultants join the same network as your computers, printers and shared folders, their devices can "see" yours. An infected phone, or just a curious guest, should not have that opportunity. A guest network is a second Wi-Fi network with its own name and password that gives access to the internet but keeps visitors out of the internal network.

As a bonus, the password of your main network stays private: you never have to share it, or change it when someone leaves.

What do you need to switch it on?

A router or access point that supports the feature. Many office and home models offer it, but the menu name varies by brand: look for "Guest", "Guest Network" or "Guest Access".
Administrator access to the router. If you don't remember the password, it is usually printed on the device label or was set by whoever installed the line.
The router must be the one actually managing the network. If a second router sits behind it in "client" or "repeater" mode, the guest feature may not be available: on some ASUS models, for example, it only works in router mode.

If your device doesn't have this feature, the fix is a newer access point or router that includes it.

How do you create the guest network on a FRITZ!Box?

The FRITZ!Box is very common in Italy. In the device's user interface:

Open Wi-Fi → Guest Access.
Enable guest access.
Choose Private Wi-Fi guest access (password-protected). There is also a Public Wi-Fi hotspot without a password, but it is not suitable for an office, because data is unencrypted unless the guest's device supports OWE.
Pick the network name (SSID) so it is easy to recognise, for example "Office-Guests", and a secure encryption method, such as WPA2 or WPA3.
Set a password of 8 to 63 characters.
Open Additional Settings, review the options below, then click Apply.

Entries may be named slightly differently depending on the model and software version (FRITZ!OS).

Which options are worth a look?

Automatic disable: turns the guest network off after a set time, handy if you only use it for meetings.
Wireless devices may communicate with each other: leave it off, so one guest cannot reach another guest's device.
Restrict internet applications: limits guests to browsing and email.
Display Captive Portal: shows a welcome page before guests can browse.

The FRITZ!Box keeps guest devices fully separated from those on the main network. Be aware that while guest access is on, features such as the MAC address filter, port sharing and telephony are not available to guests.

How do you block access to the internal network on an ASUS router?

On an ASUS router in router mode, you create the guest network from the Guest Network menu (or Guest Network Pro, depending on the model). Then make sure guests cannot reach the internal network:

Log in to the router at http://www.asusrouter.com.
Open Guest Network and choose the guest profile, or create a new one.
Find Access Intranet and disable it. In newer firmware versions the path is Network → General → Access Intranet, where you untick the main network.
Click Apply.

Available options depend on the model and firmware version: if you can't find the entry, check the router for updates.

How do you check that it works?

Connect a phone to the guest network using the password you chose.
Open any website: it should load.
Try to open the router's admin page or find the network printer: they should not be reachable.

If you can still see internal devices, reopen the settings and check that isolation is really enabled.

Sources

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Guide written with AI assistance and checked by me before publication.