How to disable IPv6 address advertisements on L2 VPN

Hi,

I have a site-to-site L2 VPN.
How can I disable to get IPv6 address via VPN?
When I turn on IPv6 address advertisement on the Site1, Site2 also get IPv6 address automatically what I want to prevent.

I tried with iptables6 rules but I could drop only ping packages while machine on the other site still got IPv6.

Thanks for your help!