I found a lot of information to handle an IPv6 over IPv4 communication, but almost nothing about IPv4 over IPv6.
Which possibilities exists integrating IPv4 over IPv6 on a Cisco Router (e.g. 881, or perhaps a Layer 3 Switch)?
Are there tunnel modes like for 6over4 (ipv6ip, gre)?
I attached a little topology to show my thoughts.
GRE IPv6 is what you're looking for.
tunnel mode gre multipoint ipv6
tunnel mode gre ipv6
You can do on top IPv6 GRE over IPsec with IPv4 payload.
On ASA on top exist the possibility to have IPv4 traffic natively in IPv6 when doing IPsec (limited support)