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

[Alexandre Petrescu <[e-mail]>]

Le 24/02/2017 à 18:53, Christopher Morrow a écrit :
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> On Fri, Feb 24, 2017 at 12:09 PM, Alexandre Petrescu
> <[e-mail] <mailto:[e-mail]>> wrote:
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>     Le 24/02/2017 à 17:27, Christopher Morrow a écrit :
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>         On Fri, Feb 24, 2017 at 10:48 AM, Alexandre Petrescu
>         <[e-mail]
>         <mailto:[e-mail]>
>         <mailto:[e-mail]
>         <mailto:[e-mail]>>>
>         wrote:
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>         Le 24/02/2017 à 15:59, Christopher Morrow a écrit :
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>
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>         On Fri, Feb 24, 2017 at 9:09 AM, Alexandre Petrescu
>         <[e-mail]
>         <mailto:[e-mail]>
>         <mailto:[e-mail]
>         <mailto:[e-mail]>>
>         <mailto:[e-mail]
>         <mailto:[e-mail]>
>         <mailto:[e-mail]
>         <mailto:[e-mail]>>>> wrote:
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>         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?
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>         I don't think this matters... 'end users' will in almost all cases
>         just attach and get connectivity.
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>         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?
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>         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.
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>         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.
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>     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.
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>     I guess the same bug is is in BSD, linux and what have you.
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> yes, I think so.. for linux:
> $ sudo ip -6 addr add 2001:700:4::1 dev em1
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> gets me:
>  inet6 2001:700:4::1/128 scope global

That address is good, but how about the routing table?  Does it get an 
entry like 2001:700:4::/64?

> so that actually seems correct.
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>         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.
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>         I assume you assume that ip/ifconfig by consenting adults means the
>         adults type a plen in the CLI, right?
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>         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.
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>     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.
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>
> ok
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>         That makes it mandatory that the CLI _requires_ a plen, right?  That
>         CLI should not allow silence for a plen parameter.
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>         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!!
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>         don't rely on defaults.
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>     I agree.
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>         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.
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>         correct, so.. be specific in your configuration effort please...
>         which again, means that the 'what is the default?" conversation is
>         moot.
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>     I am not asking what is the default.
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>     I am saying that apparently numerous implementations out there consider
>     the default to be 64.  This consideration is wrong.
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> yes, I agree with you here.
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>     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 '::'.
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>     But there is by far no single standard that says the default prefix
>     length is 64.
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>     That's why it's a bug.
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>     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.
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>
> ok, cool, i think we agree on all of this at least :)

:-)

Alex

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