Re: [v6ops] IPv6-Only Preferred DHCPv4 option

Simon Hobson <linux@thehobsons.co.uk> Thu, 05 December 2019 16:17 UTC

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Subject: Re: [v6ops] IPv6-Only Preferred DHCPv4 option
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Another typo, I think. Top of page 2 it says :
"Therefore it would be beneficial for IPv6 deployment if operators could implement IPv4-mostly (or IPv4-as-a-Service) segments ..."
Should that be IPv6-mostly ?


Roy Marples <roy=40marples.name@dmarc.ietf.org> wrote:

> It assumes that IPv6 is the be-all and end-all.

It is, for all practical purposes.

> Maybe one day we will have IPv8?

Many people said "why go to so many bits for IPv6 addresses ?". The answer being (partly) so that the need for another mass migration should be a long long looooong time away - most likely long after all of us are no longer interested, and IPv4 is as common as AppleTalk, IPX, DECNet, etc !


> Mark Smith <markzzzsmith@gmail.com> wrote:

> So I haven't read the draft either, although the following applied in the context of the the IPv6-only flag draft and I think this one.
> 
> Why aren't IPv4 (and IPv6) addresses acquired on-demand when the first application opens an IPv4 (or IPv6) socket, and then released when the last application closes the last IPv4 socket?

Just think about it.
An application starts, and wants to know what protocols it can use - it can't unless something else has forced addresses to be assigned.
Or it needs to know what addresses are available (perhaps it's configured to use only certain addresses) - it can't unless something has forced them to be assigned.
The host (or administrator of it) may wish to apply firewall rules - bit tricky if there's no protocols active !

When starting an application, the user would have a further delay while an address was obtained and configured. And what address family would the system configure ? Would it do the initial DNS request to the IPv4 server it gets from the DHCP4 server ? Or would it send it to the IPv6 server it gets from RAs ? Would it wait for "long enough" to know what address families are available, or just use the first that came up ?

What about Bonjour/mDNS/Zeroconf ? Would you suppress them until needed ? How would another device connect to a service offered on this host if you suppressed configuring interface(s) and sending mDNS advertisements until something local needed it ?

In reality, most systems (as a whole, taking into account everything running on them) are so chatty that the host would be forced to obtain and configure addresses of all families on all interfaces pretty well as soon as it's started up.


Simon