L2TP ppp-options ipv6 does not work without ipv6 pool, but it should as we can get such addresses via RADIUS attributes:
Framed-IPv6-Prefix and Delegated-IPv6-Prefix
Example of config
set vpn l2tp remote-access authentication mode 'radius' set vpn l2tp remote-access authentication radius dae-server ip-address '127.0.0.1' set vpn l2tp remote-access authentication radius dae-server port '1700' set vpn l2tp remote-access authentication radius dae-server secret 'testing1234' set vpn l2tp remote-access authentication radius server 192.0.2.5 key 'key123' set vpn l2tp remote-access client-ip-pool start '203.0.113.10' set vpn l2tp remote-access client-ip-pool stop '203.0.113.100' set vpn l2tp remote-access client-ip-pool subnet '203.0.113.0/24' set vpn l2tp remote-access ppp-options ipv6 'allow'
check config
vyos@r1# cat /run/accel-pppd/l2tp.conf | grep ipv6 ipv6pool ipv6_nd ipv6_dhcp [edit] vyos@r1#
expecting ipv6=allow