Re: [PATCH] network: allow accept_ra == 0 when enabling ipv6 forwarding

On Wed, Aug 12, 2020 at 07:21:14PM -0400, Laine Stump wrote: Heh, ipv6 in my work VM is my white whale, so, call me Ishmael :) Interesting, from a cursory search the only place NetworkManager seems to set accept_ra to 1 is [1] for ip tokens (TIL ...) and then that seems to turn if off again when the interface is enabled. But you know, that's also 18,000+ lines of logic in there ... so ... NM that reads those files and basically passes them as config into NM "core". So it doesn't do anything particularly magic. However I'm reminded of a bug that took us a very long time to diagnose with "glean", a tool to configure interfaces from config-drive data in OpenStack clouds. Some clouds don't do DHCP, so it is used to read the config-drive data set by the cloud and write out the network config. It had a long history, before systemd udev activation was a thing, an was calling "ip link set dev <interface> up" on the interface and then seeing if it had a carrier. This would enable accept_ra == 1 and the kernel would configure an IPv6 address; however since the interface then looked configured, and NetworkManager would ignore it, and thus not apply the IPv4 configuration we had written out. Hosts came up with an IPv6 but no IPv4; it was all very confusing till we put it together. My long winded point being that *maybe* something else is getting in the way ... So the intent at least is to do this warning iff the existing interface is already set to "1". So if you did put that bridge into the VM network and we enabled forwarding on it, that would seem to change it's behaviour and possibly break it? ++ to that, if the correct response is to error, or automatically set it to "2", or ignore it are all open questions :) -i [1] https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/52af5... [2] https://review.opendev.org/#/c/688031/