Unable to connect Dual Stack subscriber when using BNG CGNAT and Dual stack in the same VRF.

Dual Stack subscribers under a VRF with CGNAT will not connect.

The RPF-check for IPv6 does not allow dual subscribers to connect.

1. Configure a firewall filter for IPv6 allowing destination IPv6 address ff02::1:2/128 and port 547.

   [MASTER]
lab@MXtest1> show configuration firewall family inet6 filter rpf-pass-dhcpv6                  

   term allow-dhcp {
 from {
        source-address {
            fe80::/10;
        }
        destination-address {
            ff02::1:2/128;
        }
    }
    then {
        count COUNT-ALLOW_DHCP_BOOTP;
        accept;
    }
}
term DENY-FAILED_RPF {
    then {
        count COUNT-DENY_FAILED_RPF;
        reject;
    }
}

2. Then apply this IPv6 firewall filter to the rpf-check under the corresponding dynamic-profile.

   [MASTER]
   	lab@MXtest1> show configuration dynamic-profiles CGNAT_DS interfaces 
   	pp0 {
   	    unit "$junos-interface-unit" {
   	        no-traps;
   	        ppp-options {
   	            pap;
   	        }
   	        pppoe-options {
   	            underlying-interface "$junos-underlying-interface";
   	            server;
   	        }
   	        keepalives interval 30;
   	        family inet {
   	            rpf-check;
   	            unnumbered-address lo0.1;
   	        }
   	        family inet6 {
   	            rpf-check fail-filter rpf-pass-dhcpv6;   
   	            address $junos-ipv6-address;
   	        }
   	    }
   	}

3. Subscribers will now connect on a VRF with CGNAT and Dual-stack.

   [MASTER]
   lab@MXtest1> show subscribers    
   Interface           IP Address/VLAN ID          User Name             LS:RI
   pp0.3221225479      10.100.100.6                CGN-DS           default:NAT-44D      
   *                   2001:1208:ffff:5::/64
   *                   fdff:ffff:0:3::/64
   pp0.3221225479      2001:1208:ffff:5::/64            
   default:NAT-44D    
   

2021-04-19: Updated step one in the solution.