SlackBuildsOrg/network/shorewall6

shorewall (IPv6 support package for shorewall)

The Shoreline Firewall, more commonly known as "Shorewall", is a Netfilter
(iptables) based firewall that can be used on a dedicated firewall system, a
multi-function gateway/router/server or on a standalone GNU/Linux system.

As of version 4.5, shorewall consists of 3 packages: 
* shorewall-core, contains the common elements to both IPv4 and IPv6 components
* shorewall, the IPv4 component
* shorewall6, the IPv6 component

The shorewall-core package is needed for both but now you can install the IPv6
packages without needing the IPv4 one if you are on aIV6 network only.