Limit access from WAP to specific IP

I’m opening some ports for forwarding to an asterisk server (as usual 5060 and 10000)
VOIP provider is recommending to limit access to asterisk only to their IP.
How do I limit the access to a single WAN IP or to a range ?

To be clear, you want to limit only one IP or IP range accessible to the port 5060 and 10000 on WAN?

You can go to Luci->firewall->traffic rules, find your port forward then edit it. You will have a lot of options.

More advanced, you can try some IP tables skills. Like this one: