Why the router connects to akamaitechnologies.com?

[Giorgio74]

Hello,
I've an ASUS RT-AC87U router with Merlin firmware 380.65_2 installed.
When I issue the netstat command from the GUI I can see that the router has several sessions estabilished with deploy.akamaitechnologies.com

tcp        0      0 192.168.1.4:38616       2.21.89.67:www          ESTABLISHED
tcp        0      0 192.168.1.4:52311       a88-221-132-166.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:53973       a88-221-132-177.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:53970       a88-221-132-177.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:53971       a88-221-132-177.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:33077       a88-221-132-176.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:54974       a88-221-132-176.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:43042       a88-221-132-177.deploy.akamaitechnologies.com:www ESTABLISHED
tcp        0      0 192.168.1.4:43042       a88-221-132-177.deploy.akamaitechnologies.com:www ESTABLISHED

The source IP 192.168.1.4 is my asus router's WAN IP address (it is behind the ISP modem router) thus if I'm not worng it means that it is the router itself having that sessions estabilished. This seems also to be confirmed by the fact that I see none of them if I use netstat-nat tool.
I've also added an url filter for "akamaitechnologies.com" on the firewall's url filter but even after rebooting the router they are still there
Why my router connects itself to them?

Thank you!
Giorgio