dhcpcd-discuss

On 08/03/2018 22:31, Brenden Blanco wrote:
> > I'm running dhcpcd on a single interface in dual stack and IPv6-PD.
> > Archlinux recently updated to 7.0.1 which broke IPv6 for me.
> >
> > After doing git bisect I found that commit ef53a17 (DHCPv6: listen on all
> > IPv6 addresses for active interface) responsible for this. Reverting it on
> > master solves the issue for me.
> >
> > I'm running archlinux with systemd-networkd for everything else but the WAN
> > interface.
> > I can provide additional information if needed.
>
> I came across this thread while googling, and I believe that I am
> hitting it as well. Specifically, it seems that my ISP (wave-G
> broadband) is ignoring any solicit requests that do not come from port
> 546 (packets are blackholed).
>
> Besides reverting ef53a17, could we consider introducing a config
> option to allow the source port to be overridden, as a buggy ISP
> workaround?

The problem here is simple, but hard to solve.
dhcpcd is not running in master mode, which means you could have >1 
dhcpcd instance handling dhcp6 on different interfaces. However, only 
one instance can actually bind the unspecified address to port 546. As 
we don't know which instance can win, we just don't bind it in non 
master mode, so the source port is random.

We could bind to the LL address for the interface, but that in turn 
means we *may* not be able to unicast messages to the DHCPv6 server if 
it's asking for that.
So a short term fix would be to ignore the unicast option in non master 
mode and bind to the LL address.

I'm quite busy on other things atm, but I'll try fix this soon.

Roy