(usagi-users 00619) Re: problems with usagi-kernel

[JINMEI Tatuya / 神明達哉 <jinmei@xxxxxxxxxxxxxxxxxxxxx>]

>>>>> On Thu, 05 Jul 2001 17:13:27 +0900, 
>>>>> Jun-ichiro itojun Hagino <itojun@xxxxxxxxxx> said:

>>> "ff02::1%interface").  the address ff02::1 itself is ambiguous to
>>> the kernel.
>> Is it mandatory to specify interface?

> 	I believe it is.  if the user specifies nothing, it is indeed ambiguous
> 	to the kernel.  the user can see unexpected results, if the user thinks
> 	differently from the kernel.

Agreed, but it depends on what you mean by "mandatory".

As for specification, it is not very clear.  But
draft-ietf-ipngwg-scoping-arch-02.txt mentions the notion of the
"default scope zone":

   An implementation should also support the concept of a "default" zone 
   for each scope.  It is convenient to reserve the index value zero, at 
   each scope, to mean "use the default zone".  This default index can 
   also be used as the zone qualifier for an address for which the node 
   is attached to only one zone, e.g., when using global addresses. 

As for implementation, at least KAME does not explicitly mandate to
disambiguate the scope zone (although it is hard for beginners to
understand the behavior correctly).  I'm not sure much about other
implementations.

>> What would be happend if we didn't specify an interface?

> 	the following stories are just for KAME kernel.  not sure if it is
> 	the right thing to do.  i guess not...
> 	- if there's no special configuration, it will follow the routing table.
> 	  in most cases, it would follow the IPv6 default route, and goes out
> 	  from the default outgoing interface.

Actually, this (usually) does not work, because neighbor discovery
does not work in this case (I won't go to the details here).  However,
when the "default interface" is specified and the zone for a scoped
address is ambiguous, the KAME kernel will pick the zone on which the
default interface belongs in the scope type.  I guess the guy who
first asked the question set the default interface, which can let
him/(her?) omit the (scope) zone identifier.

In any case,

- users are not recommended to type scoped addresses (particularly
  link-local ones), unless the users are quite familiar about the
  notion of scoped addresses.
- even for expert users, I'd recommend them to disambiguate the scope
  zone in order to avoid unexpected kernel behavior, regardless of the
  existence of the "default scope zone".

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					jinmei@xxxxxxxxxxxxxxxxxxxxx