Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 option
Lorenzo Colitti <lorenzo@google.com> Fri, 06 December 2019 00:41 UTC
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From: Lorenzo Colitti <lorenzo@google.com>
Date: Fri, 06 Dec 2019 09:41:29 +0900
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To: Roy Marples <roy@marples.name>
Cc: Ted Lemon <mellon@fugue.com>, Tomek Mrugalski <tomasz.mrugalski@gmail.com>, dhcwg@ietf.org, V6 Ops List <v6ops@ietf.org>, draft-link-dhc-v6only@ietf.org
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Subject: Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 option
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On Thu, Dec 5, 2019 at 11:48 PM Roy Marples <roy@marples.name> wrote: > The *something* else is probably IPv6 but I don't see why this RFC > should mention it other than a use case. > There is actually a reason why the option is specific to IPv6. Here's why. The primary reason for the existence of option is that hosts (especially moblie hosts) don't want to wait to find out what's available before they make networking available to applications. This is why when they connect they initiate IPv4 and IPv6 (and whatever else they have) in parallel. The option as written conveys two important bits of information to the host: 1. The network would prefer the host not use IPv4 if the host has something else available. 2. Something else *is available* on this network, so the host is not going to wait forever for it. In the current draft, "something else" is specifically IPv6 (because not really any other credible alternative to IPv4) and more specifically, IPv6 with NAT64 (because there is no other IPv6 transition mechanism that is widely implemented in hosts today - all the others are implemented in the network). I think you're saying that this option should mean "I'd prefer you not use IPv4 except as a last resort" option, as opposed to "I'd prefer you use IPv6 instead". What that means is that the option will only be providing #1 and not #2. I think it's worse that what we are currently proposing. The reasons are: 1. If we make this an "IPv4 as last resort" option, a client that gets the option is not being told if there is anything else available. So, say that the administrator sets this option because they want hosts to prefer IPX (or netbeui, or appletalk, or whatever) over IPv4. What if the host doesn't support/use any of those protocols, but only supports IPv6, which is the overwhelmingly common case today? The host doesn't really have a clear path forward. The only thing it can do is try IPv6 "for a while", and then go back to DHCPREQUEST (assuming the offer is still valid, and if not go back to DHCPDISCOVER), and use IPv4 anyway. That seems like a bad user experience. 2. If we make this an "IPv4 as a last resort option" instead of a "please use IPv6" option, is that hosts will simply assume that the option means "please use IPv6". Even though this assumption is technically incorrect, if enough hosts do it, from a deployment perspective it won't matter, because network operators won't be able to use this option code for anything other than IPv6-only networks. That outcome is worse than if we had explicitly defined this as a "please use IPv6" option, because well-behaved hosts will have to incur the additional complexity to build the technically correct implementation that can never be used in practice. If we really don't want to make this option specific to IPv6, then we can define an option that can convey multiple alternatives. In other words, the option would mean "please don't use IPv4 if you support any of the alternative protocols listed in this option". We could initially define an alternative code only for "IPv6-only with NAT64", but if later some other protocol comes along, or some other IPv6 transition mechanism becomes widely deployed on hosts, we could add a code for it. Personally I don't think this is worth the engineering complexity because I don't see any other credible alternative than IPv6-only with NAT64, but I would much prefer it over an option that doesn't say anything at all about what else is available.
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Philip Homburg
- [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Bjørn Mork
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Tommy Pauly
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Michael Richardson
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Fred Baker
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… David Farmer
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… David Farmer
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Roy Marples
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Mark Smith
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Roy Marples
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Mark Smith
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Bjørn Mork
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Michael Richardson
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Michael Richardson
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Roy Marples
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Roy Marples
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option mohamed.boucadair
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Michael Richardson
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Bernie Volz (volz)
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Jen Linkova
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Lorenzo Colitti
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Mark Smith
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Fred Baker
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Tomek Mrugalski
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Tomek Mrugalski
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Tomek Mrugalski
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Tomek Mrugalski
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Tomek Mrugalski
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Tomek Mrugalski
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option Lorenzo Colitti
- Re: [dhcwg] IPv6-Only Preferred DHCPv4 option STARK, BARBARA H
- Re: [dhcwg] [v6ops] IPv6-Only Preferred DHCPv4 op… Ted Lemon