In my test environment, I noticed that the default gateway for IPv6 is changed from 1 to 0,

is this correct?

Reproduce steps are:

* openstack cli:

openstack network create test-ipv6-net

openstack subnet create --subnet-range 2001:db8::200:0/64 --ip-version 6 --ipv6-ra-mode dhcpv6-stateful --ipv6-address-mode dhcpv6-stateful --network test-ipv6-net test-ipv6-subnet

# the gateway_ip in the output is 2001:db8::200: but 2001:db8::200:1 is the expected IP

* neutron cli:

neutron net-create test-v6

neutron subnet-create --name test-v6-subnet --ip-version 6 test-v6 2002:db8::200:0/64

# the gateway_ip in the output is 2001:db8::200: but 2001:db8::200:1 is the expected IP

there are 3 versions of OpenStack I've tested, the results are:

OpenStack Rocky: 2001:db8::200:1

OpenStack Train: 2001:db8::200:1

OpenStack Wallaby: 2001:db8::200:

the virtual router will use the gateway ip for port, and some hardware networking sdn controller for neutron may not work.