ESS Customer Verizon is testing RHOSP 17.1 (therefore RHEL 9.2) and has encountered an issue where "IPV6_AUTOCONF=no" gets ignored in ifcfg file.

In sosreport ./0080-sosreport-rchltxeldnce-h-pe5dloc-0-03779789-2024-04-03-ippoyfb.tar.xz/sosreport-rchltxeldnce-h-pe5dloc-0-03779789-2024-04-03-ippoyfb/etc/sysconfig/network-scripts/:
~~~
$ cat ifcfg-eth4

This file is autogenerated by os-net-config
DEVICE=eth4
ONBOOT=yes
HOTPLUG=no
NM_CONTROLLED=no
MTU=1480
IPV6INIT=yes
IPV6_MTU=1480
IPV6_AUTOCONF=no
IPV6ADDR=2607:f160:a:7804:124::9000/64
DNS1=2607:f160:a:7804:12::8047
~~~

But we still see the local configured IPv6 fe80::5054:ff:fe4b:8881/64, and because the gateway is doing route advertisement the default gateway is set with local IPv6 of the gateway:
~~~
6: eth4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1480 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:4b:88:81 brd ff:ff:ff:ff:ff:ff
altname enp5s0
inet6 2600:80b:210:5801::8001/64 scope global
valid_lft forever preferred_lft forever
inet6 2600:80b:210:5801::1000/128 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe4b:8881/64 scope link
valid_lft forever preferred_lft forever
~~~

from troubleshooting ifup-ipv6 we see autoconfig and accept_ra are disabled:
~~~
+ /sbin/sysctl -e -w net.ipv6.conf.eth4.forwarding=0
+ /sbin/sysctl -e -w net.ipv6.conf.eth4.accept_ra=0
+ /sbin/sysctl -e -w net.ipv6.conf.eth4.accept_redirects=0
+ /sbin/sysctl -e -w net.ipv6.conf.eth4.autoconf=0
~~~

also the default for all interfaces is disabled, but we see local IPv6 on all of them
~~~
from /etc/sysctl.d/99-tripleo.conf :

net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.default.accept_ra=0
net.ipv6.conf.all.autoconf=0
net.ipv6.conf.default.autoconf=0
~~~

also cloud config is disabled:
~~~
$ cat ./etc/cloud/cloud.cfg.d/99-tripleo-disable-network-config.cfg
network:
config: disabled
~~~

Version-Release number of selected component (if applicable):
The setup is RHOSP 17.1, therefore RHEL 9.2 with:
openstack-network-scripts-10.11.1-6.el9ost.x86_64

How reproducible:
Always

Steps to reproduce
On customer setup, deploy RHOSP 17.1, with templates that specify parameters seen in ifcfg-eth4 above

Expected results
"IPV6_AUTOCONF=no" is taken into account

Actual results
We can see that "IPV6_AUTOCONF=no" gets ignored

Expected results:

Additional info: