To block UDP port 500, kindly follow these steps:

1. Connect your device to the G34 network.
2. Open a web browser and enter http://192.168.0.1 in the address bar.
3. You will be directed to the login page of the web interface (GUI).
4. Log in using your credentials.

During the initial setup of the G34, you’ll be prompted to create a password for accessing the web interface. If you’ve set up the Surfboard Central app, it will generate the password automatically for you

To retrieve the password for the web interface through the Surfboard Central app, please can refer to the following link. 

http://arris.force.com/consumers/articles/General_FAQs/SURFboard-Central-Web-Manager-Access

After logging in, please follow these required steps:

1. Select Parental Control > Managed Services.
2. Select Add 
3. Enter the port number and ensure that the option for 'Always Block' is turned on.

Thank you for your reply. After some browsing around on the Parental Control and other options I did locate the page to set protocol and port to block. In fact blocking is working as expected.

One related question I still have is about blocking a particular site: https://discord.com. Under Parental Control->Managed Sites I tried to block, but it does connect to that site even after restarting router after it has been blocked. It does get blocked after some random time interval, and I have seen it getting unblocked, unlike other blocked sites.

It seems discord.com connects to (through) multiple IPv4 addresses, which I retrieved, but is it possible to do destination IPv4 address filtering?  Thanks for any help.