Re: [ssm] permanent ipv6 ssm addresses [was ...last call..]

[Brian Haberman <[e-mail]>]

Hugh Holbrook wrote:
> [snipping just the thread on allocating permanent ipv6 addresses]
> 
> Thanks for your input, Pekka and Brian.
> 
> Exactly -- the idea is that an application that requires, for some
> reason, that the same channel destination address be used on all hosts
> providing that channel would be allocated from 0x40000000-0x7fffffff.
> Any other channel destination addresses, regardless of lifetime, must
> come from the 0x80000000-0xffffffff space.
> 
> Section 4.3 states that a host OS SHOULD provide an interface to
> allocate a random address, and that this information must be stored in
> a database that persists across reboots.  The idea is that this is the
> mechanism that an application or user uses to allocate an SSM address.
> 
> I think this is probably already clear, but I want to underscore the
> importance of using random allocation for SSM addresses.  It is not a
> good idea (and is in fact specifically disallowed in section 4.3) for
> a host, host application, or host OS, to deterministically pick
> FF3x::1 or FF3x::2, or *any* fixed value as the channel destination
> address on all hosts for some application -- because of the link-layer
> collision issue.
> 
> --------------------------------
> 
> So to summarize on the text changes, the only textual change I
> currently think is warranted is to clarify in 4.3 and in the IANA
> Considerations section the use of the 4000:0000 to 7fff:ffff
> 
> In 4.3, change this:
> 
>   The SSM destination address 232.0.0.0 is reserved, and systems MUST NOT
>   send datagrams with destination address of 232.0.0.0.  The address range
>   232.0.0.1-232.0.0.255 is currently reserved for allocation by IANA.  The
>   IPv6 SSM address range FF3x::/32 is reserved for IANA allocation.
> 
> to correctly call out the 0x4000000-7fffffff range.
> 
>   The SSM destination address 232.0.0.0 is reserved, and systems MUST NOT
>   send datagrams with destination address of 232.0.0.0.  The address range
>   232.0.0.1-232.0.0.255 is currently reserved for allocation by IANA.  SSM
>   destination addresses in the range FF3x::4000:0000 through
>   FF3x::7FFF:FFFF are similarly reserved for IANA allocation.

Seems reasonable to me.

> 
> I'm not sure where the FF3x::/32 came from, but I think it is a
> vestige of an earlier revision that was less clear on the /96 vs /32 
> distinction.

I agree.  RFC 3306 reserves the entire /32 so that group IDs can
grow beyond the lower 32 bits of the group address.  RFC 3307 then
states that allocations must be done out of the /96 (for the time
being).

> 
> And a similar fix IANA Considerations.
> 
>   Addresses in the range 232.0.0.1 through 232.0.0.255 and IPv6
>   addresses with prefix FF3x:: are reserved for services with wide
>   applicability that either require or would strongly benefit if all
>   hosts used a well-known SSM destination address for that service.
> 
> to read
> 
>   Addresses in the range 232.0.0.1 through 232.0.0.255 and IPv6
>   addresses in the range FF3x:4000:0000 to FF3x::7FFF:FFFF are
>   reserved for services with wide applicability that either require or
>   would strongly benefit if all hosts used a well-known SSM
>   destination address for that service.
> 
> Any objections to these changes?

I don't have any objections.

Brian

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