Re: [v6ops] IPv6-Only Preferred DHCPv4 option

[Lorenzo Colitti <[e-mail]>]

On Thu, Dec 5, 2019 at 9:53 AM Mark Smith <[e-mail]> wrote:

> If hosts only acquired IPv4 addresses via DHCPv4 based on when the first
> IPv4 application started running, then when a host is only running IPv6
> only applications, it would never acquire an IPv4 address because it
> wouldn't need one, meaning never try to use DHCPv4 (so would avoid the
> link-layer broadcast DHCP_DISCOVERS) and never use ARP (avoid link-layer
> broadcast ARP Requests).
>

Speaking as an OS implementer: how do I know whether an application is an
IPv4 application?

   - When it calls getaddrinfo() with AF_UNSPEC? Pretty much all apps do
   that.
   - When it creates an IPv4 socket? But what if it's creating an IPv4
   socket for the purpose of connecting to another network on the system
   (e.g., cellular data) that does have IPv4?
   - When it does a connect() on an IPv4 socket? But what if that's just a
   happy eyeballs stack that is using IPv4 because it might be available?
   - What if the app knows it needs IPv4 and will refuse to do any
   networking if it doesn't find an IPv4 address on the system?