Re: [v6ops] draft-ietf-6man-rfc4291bis prohibiting non-/64 subnets

[Alexandre Petrescu <[e-mail]>]

Le 24/02/2017 à 17:27, Christopher Morrow a écrit :
>
>
> On Fri, Feb 24, 2017 at 10:48 AM, Alexandre Petrescu
> <[e-mail] <mailto:[e-mail]>>
> wrote:
>
>
>
> Le 24/02/2017 à 15:59, Christopher Morrow a écrit :
>
>
>
> On Fri, Feb 24, 2017 at 9:09 AM, Alexandre Petrescu
> <[e-mail] <mailto:[e-mail]>
> <mailto:[e-mail]
> <mailto:[e-mail]>>> wrote:
>
>
> A question to Windows is the following: what prefixlen does it set
> when the end user manually assigns an address on an interface
> without specifiying a prefixlen?
>
>
> I don't think this matters... 'end users' will in almost all cases
> just attach and get connectivity.
>
>
> Let me go next in cycle: what does linux do when one ifconfig add an
> IPv6 address without telling the plen?  Is it adding an entry in the
> rt table?  Which plen?  Is that plen normal?
>
>
> still don't think this matters. If a user messes up what they type,
> they messed up. if the instructions aren't complete, they aren't
> complete and there will be mistakes. An interface configuration
> requires all proper parameters be set, or problems will arise.
> Assumptions about current and future behavior are proven wrong time
> and again.
>
> non-deterministic behavior over time is the hallmark of this
> space... please do not rely on defaults for hand-managed/bespoke
> configurations if you expect things to work reliably and repeatably.

That means the following: Windows please make the plen parameter
mandatory.  Dont leave it optional only to subversively set it to 64.
That's a software bug because nobody asks you to set the plen to 64 when
the end user does not specify one.

I guess the same bug is is in BSD, linux and what have you.

>
> If they are in a place where someone says: "Hey, you should go
> if/ipconfig ...." then .. they are 'consenting adults' and can do
> whatever they please.
>
>
> I assume you assume that ip/ifconfig by consenting adults means the
> adults type a plen in the CLI, right?
>
>
> sure, or a script/program/etc does this, it's not important how the
> 'ifconfig' happens, it's important that when it happens the right
> parameters are passed to the 'ifconfig' command.

I agree.  If 'ifconfig' silently assumes 64 then that assumption is
wrong.  The ifconfig programmer should take that as a software bug.
It's not an RFC that requires them to put 64 there.

> That makes it mandatory that the CLI _requires_ a plen, right?  That
> CLI should not allow silence for a plen parameter.
>
>
> sure, or you are at the mercy of the implementor of that command:
> Today I like /64! It's tomorrow and now I like /62!!
>
> don't rely on defaults.

I agree.

> Because silent plen means 64.  And I dont think it's right to assume
> a by-default 64 plen.  Because many people think 64 is right and
> others think it's wrong, there does not seem to be a commonly agreed
> 'by default' value for plen.
>
>
> correct, so.. be specific in your configuration effort please...
> which again, means that the 'what is the default?" conversation is
> moot.

I am not asking what is the default.

I am saying that apparently numerous implementations out there consider
the default to be 64.  This consideration is wrong.

A 'default' value is something that everybody agrees with.  For example,
one can leave out '::' from a command line adding a default route and
just say 'default'.  There is an agreed standard that says that
'default' is '::'.

But there is by far no single standard that says the default prefix
length is 64.

That's why it's a bug.

It's like boxes with pre-defined passwords admin/admin.  The local
programmer imagined it a good 'default' but never asked around the
validity of such assumption.  And that creates problems.

Alex

>
>
> Alex
>
>
>
> again the proposed text (now 175+ messages back) really covers this
> already..
>
>