iocage and ipv6 in TrueNAS

[oliver.epper]

I have an observation that I cannot explain. When I create a jail with the web-gui and configure it to use vnet, dhcp and slaac I get the following config-file:

```pre
{
"bpf": 1,
"cloned_release": "13.2-RELEASE",
"dhcp": 1,
"host_hostname": "test",
"host_hostuuid": "test",
"ip6_addr": "vnet0|accept_rtadv",
"jail_zfs_dataset": "iocage/jails/test/data",
"last_started": "2024-02-27 13:59:19",
"release": "13.2-RELEASE-p9",
"vnet": 1,
"vnet0_mac": "1e1b0dae1b75 1e1b0dae1b76",
"vnet_default_interface": "auto"
}
```

and the jails `/etc/rc.conf` looks like:

```pre
[...]
# Enable IPv6
ipv6_activate_all_interfaces="YES"
rtsold_enable="YES"
```

When I start the jail though `/etc/rc.conf` becomes:

```pre
[...]
# Enable IPv6
ipv6_activate_all_interfaces="YES"
rtsold_enable="YES"
ifconfig_epair0b="SYNCDHCP"
ifconfig_epair0b_ipv6="inet6 auto_linklocal accept_rtadv autoconf"
```

The jail has working ipv6. LL, ULA and Internet address all perfectly configured. If I do the same setup with a freshyl installed iocage on a FreeBSD-14.0-RELEASE the jails `/etc/rc.conf` remains unchanged and I get neither an ULA not and internet ip. My question: What process (or mechanism) changes the content of `/etc/rc.conf` in TrueNAS? Where can I find the jail configuration (and the usage of iocage) in the TrueNAS source?

For context: I am evaluating naked FreeBSD instead of TrueNAS because I prefer FreeBSD and I want 14.0. Don't get me wrong. TrueNAS ist a fantastic product that I am using for quite some time, now. It's just that I want FreeBSD and TrueNAS is so clearly heading to Linux. I bet TrueNAS Scale is (or will become) a great successor. But I want FreeBSD.