Re: [dhcwg] RFC 8925 on IPv6-Only Preferred Option for DHCPv4

Roy Marples <> Sun, 25 October 2020 20:06 UTC

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From: Roy Marples <>
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Date: Sun, 25 Oct 2020 20:06:10 +0000
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Subject: Re: [dhcwg] RFC 8925 on IPv6-Only Preferred Option for DHCPv4
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On 17/10/2020 13:53, wrote:
> A new Request for Comments is now available in online RFC libraries.
>          RFC 8925
>          Title:      IPv6-Only Preferred Option for DHCPv4

Just reading through this and I find this in section 3.2

The IPv6-Only Preferred option SHOULD be included in the Parameter Request List 
in DHCPREQUEST messages (after receiving a DHCPOFFER without this option, for an 
INIT-REBOOT, or when renewing or rebinding a leased address). If the DHCPv4 
server responds with a DHCPACK that includes the IPv6-Only Preferred option, the 
client's behavior depends on the client's state. If the client is in the 
INIT-REBOOT state, it SHOULD stop the DHCPv4 configuration process or disable 
the IPv4 stack completely for V6ONLY_WAIT seconds or until the network 
attachment event, whichever happens first. It also MAY send a DHCPRELEASE 
message. If the client is in any other state, it SHOULD continue to use the 
assigned IPv4 address until further DHCPv4 reconfiguration events.

It's the last line of the paragraph which is of interest. It implies that this 
option only works in the INIT-REBOOT state. The lack of the SELECTING state is 
pretty glaring but a minor omission.

Am I correct in thinking that RENEWING and REBINDING states pretty much ignore 
this option if it was absent and is now present? Or is the intent to stop using 
the address when in these states as they are "DHCPv6 reconfiguaration events"?
Or just wait until it naturally expires? It's not clear what the expected action 
here should be.