On a Saturday in 2025, Chimmie Firefly via Users wrote:
Hello,
Hello.
I have an issue whenever using `/proc/sys/ipv6/conf` as read-only
mountpoint.
May I ask why? Essentially you're asking libvirt to both manage and not
manage your network :)
While the libvirt by itself is running fine, I'm unable to create
NAT network interfaces because of the following error:
```
2025-07-05 19:33:32.821+0000: 100: error : networkSetIPv6Sysctl:1847 : cannot write to
'/proc/sys/net/ipv6/conf/virbr0/disable_ipv6' on bridge 'virbr0':
Read-only file system
The code dealing with this expects `disable_ipv6` to be writable if it
exists, same with `accept_ra` and `autoconf`
2025-07-05 19:33:32.841+0000: 100: error : virNetDevSetIFFlag:601 :
Cannot get interface flags on 'virbr0': No such device
2025-07-05 19:33:32.947+0000: 100: error : virNetlinkDelLink:688 : error destroying
network device virbr0: No such device
```
While using iproute2 and bridge utils, I'm able to create and configure new bridge
device, along with attaching the VM to the interface.
I've used the following commands:
```
sysctl -w net.ipv4.ip_forward=1
brctl addbr br0
ip link set br0 up
ip addr add 192.168.100.1/24 dev br0
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i br0 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o br0 -m state --state RELATED,ESTABLISHED -j ACCEPT
```
Is libvirt allowing to disable sysctl calls in the configuration files? If so, what should
I set in the config?
In general, no. And it also does not seem possible in this particular
case.
Jano