GRE Tunnel to Cisco Router

[AlphaLinux]

Hi

i want to run a GRE Tunnel from pfSense (2.2.6) to a Cisco IOS Router.
The config on the Cisco router which currently runs the GRE tunnel looks like this:

interface Loopback0
no ip address
ipv6 address 2001:1Axx:xxxx::1/128
!
interface Tunnel0
description IPv6-Uplink
no ip address
ipv6 enable
ipv6 tcp adjust-mss 1424
tunnel source GigabitEthernet0/0
tunnel destination x.x.x.x

what are the steps on pfsense to run this configuration ?

feedback very much appreciated

thanks