Re: Confirmation to advance: draft-ietf-6man-ipv6only-flag-05

[Philip Homburg <[e-mail]>]

> Given as of the last draft there is an option to disable processing
> despite implementing, OS vendors can implement the draft and do
> what they think suits their users.   Even more so they might leave
> the default to off for now as an advanced option to turn on and
> with a major OS update, once the world has moved on, flip the switch
> in the future.

This draft has two perspectives:
- a network perspective (hosts trying to configure IPv4 waste bandwidth)
- a host perspective (trying to use IPv4 may impact battery lifetime)

If this draft was part of a complete discussion on what to do with IPv4 
and it became clear that this flag was required, then I would have no
problem supporting the draft.

But nobody is doing any work on what IPv4 should look like in the future.
This draft is just a small hammer looking for a nail.

Without a clear idea of where we want to take IPv4 we can see some things
happening:
- To start with the host perspective. It is very like that many network will
  not set this flag. Simply because there is no operator to decide if this
  flag can be set or not. So hosts will implement counter measures to save
  battery life even if the flag is not set.

  Then because of security risks, it makes sense for hosts to either not
  implement it of leave it off by default.

  Because there is no analysis from an IPv4 perspective, we don't actually
  know if this draft is needed and how much effect it will have. There is
  justs some hints from hosts that are not optimized to live without IPv4.

- for a network, if many hosts do not implement this flag, then the network 
  somehow has to cope. If the vast majority of the hosts do not implement
  this draft then implementing this flag in a router is mostly an accident
  waiting to happen. Something that hardly any network engineer in the 
  field can quickly diagnose. So it makes sense for routers to not implement
  this draft. Which may reinforce host behavior to not rely on this flag.

- Finally, there is an existing code point in DHCPv4 to turn of IPv4 link
  local configuration. Which is safe to implement for hosts and not hard
  to provide for router vendors.

So we have a draft that clearly makes security worse. That has operational
risks if widely implemented. And at same time anybody sane will not
implement the draft. So it probably live on as a useles flag that people will 
remember to filter on their networks.