If the clients address matches one on the routers list access is granted as usual. Before letting any device join the network the router checks the devices mac address against a list of approved addresses.
Linksys Official Support Configuring Wireless Mac Filter
What is mac address filtering. There are some legitimate cases where you can use mac address filtering on your network but it wont add additional security. In computer networking media access control mac filtering or eui filtering or layer 2 address filtering refers to a security access control method whereby the 48 bit address assigned to each network card is used to determine access to the network. It wont protect you against outsiders trying to actively crack your encryption and get onto your network. In computer networking mac filtering refers to a security access control method whereby the mac address assigned to each network card is used to determine access to the network. Mac addresses are uniquely assigned to each card so using mac filtering on a network permits and denies network access to specific devices through the use of blacklists and whitelists. Mac address filtering adds an extra layer to this process.
Mac address filtering properly used is more of a network administration feature than a security feature. Otherwise its blocked from joining. However it will allow you to choose which devices are allowed online. How to find mac address of my device. You can block third party devices from connecting to your wifi router even after spying on you. This is very simple.
Instead its more of an administration tool that you can use to control whether or not your kids can access the internet at certain times during the day or if you want to manually add devices to your network which you can monitor. Mac address filtering is an in built feature that is provided by every wifi router.