Re: dhclient vs aliases

On Mon, Jun 9, 2025 at 10:40 AM Andriy Gapon <avg@freebsd.org> wrote:
>
> On 09/06/2025 17:26, Paul Procacci wrote:
> > Re: https://forums.freebsd.org/threads/dhclient-trashing-alias-ip-address-upon-reconnect.58729/
> >
> > You can use a dhclient.conf(5) entry like this to guarantee that the
> > alias is re-applied every time the interface gets a new address from
> > DHCP (or the old lease is re-applied):
> >
> > Code:
> >
> >            alias {
> >               interface "em0";
> >               fixed-address 10.0.0.3;
> >               option subnet-mask 255.255.255.0;
> >             }
>
> Thank you!
> This should work, but it kind of kills a "single source of truth" for jail
> configurations.
>
> So, it seems that there is a quirk regarding jail+aliases and DHCP.
>
> > On Mon, Jun 9, 2025 at 10:20 AM Andriy Gapon <avg@freebsd.org> wrote:
> >>
> >>
> >> Apologies if this is a FAQ and maybe it has always been like that but I've just
> >> noticed this.
> >>
> >> A switch needed to be rebooted, so on a FreeBSD host a link went down and then
> >> up on an interface connected to the switch.
> >> Apparently triggered by those events, dhclient decided to renew the interface's
> >> IP address. Afterwards, all alias IP addresses on that interface were cleared.
> >> Just in case, the new IP address was exactly the same as the old IP address
> >> (it's "hardwired" in the DHCP server configuration).
> >>
> >> This was unhelpful because the host runs a number of jails with a simple IP
> >> configuration via aliases.
> --
> Andriy Gapon

I haven't personally tested this, but does something akin to the following work?

ifconfig_em0_alias0="DHCP"
ifconfig_em0_alias1="DHCP"


Assuming you're using dhcp addressing for single source of truths then
give this a whirl perhaps.

~Paul

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