Problem/Justification
This suggests IPv6-only operation is supported: https://www.truenas.com/blog/truenas-facilitates-the-transition-to-ipv6-only/
However:
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Disabling DHCP and not setting an IPv4 static address while leaving auto configure IPv6 enabled results in no networking
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You can’t remove the IPv4 default route from the GUI
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Not having an IPv4 default route causes Apps to fail initialisation
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DHCP option 108 (IPv6-Only Preferred) is ignored
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Does not support CLAT & XLAT464 for access to IPv4-only destinations from an IPv6-only TrueNAS
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Cannot use SLAAC on multiple interfaces
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Does not support DHCPv6
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You can set IPv6 name servers under System→Network→Network Configuration, but if you try to do the above change to disable DHCP you will be taken to another screen that marks IPv6 name servers as incorrect syntax
Impact
Cannot realistically deploy an IPv6-only TrueNAS TrueNAS despite the news release stating otherwise.
User Story
Some ISPs are deploying only IPv6 to customers to minimise CGNAT, with XLAT464 providing access to IPv4. TrueNAS is the only IPv4-preferred device in my network.
TrueNAS limits on auto-configuration are too strict. There is no technical reason why multiple interfaces cannot support DHCP & SLAAC, and IPv6 in particular is meant to be configured via SLAAC. A valid limitation could be that only a single interface should have an active default route, while still allowing multiple interfaces to auto configure.