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