Re: IPv6 static addressing

On 17/03/2018 15:54, Richard Hector wrote:
> On 17/03/18 15:36, Brian E Carpenter wrote:
>> On 17/03/2018 13:44, Richard Hector wrote:
>>> Hi all,
>>>
>>> Apologies if this is a bit off-topic, but I know there's lots of IPv6
>>> knowledge here :-)
>>>
>>> If I have an IPv6 ULA block (or several) 
>>
>> Why mention ULAs? Your question applies equally to normal (globally routeable, GUA)
>> addresses. ULA and GUA prefixes are treated exactly the same both in SLAAC and in
>> DHCPv6.
> 
> Fair call - I had more or less assumed that, and was contemplating doing
> the same thing for the GUA addresses assigned by Vodafone (FibreX) -
> except that prefix is dynamic. But I know my knowledge is incomplete,
> and the general rule of asking questions on lists is to provide whatever
> info might be useful.
> 
>>> using SLAAC, and I want to
>>> additionally give out some static addresses in one or more of those
>>> blocks, am I right in thinking I can pick anything I like as long as it
>>> doesn't have the magic fffe in the middle?
>>
>> As far as I can see you can pick any valid /128 address in the applicable
>> /64 prefix. The probability of a clash with a SLAAC-generated address
>> is minimal, and duplicate address detection works.
>>
>> I don't see where :fffe: comes in any more, we dropped the model of
>> making up the interface identifier from the MAC address long ago.
>> Modern operating systems just use a pseudo-random 64 bits. Generally
>> people seem to use small integer identifiers for servers.
>> smtp.gmail.com is 2404:6800:4008:c00::6c for example.
> 
> Ok - I clearly need a better source of current IPv6 info than arbitrary
> web search results :-) Any tips? Hmm, perhaps
> https://www.apnic.net/community/ipv6-program/ipv6-bcp/ is a good start.

I think it's time the books written a few years ago were updated.
There are a lot of books: https://ipv6.net/books/
but I'm not sure any of them are current.
 
> I notice that all my addresses do have fffe in them though, and at a
> quick glance are based on the MAC address (Linux - debian stretch).
> Maybe there's a feature I need to enable.
> net.ipv6.conf.eth0.use_tempaddr looks like it; presumably it won't argue
> with my static allocations.

Probably. I installed Linux Mint a few months ago on a machine and it came
up using pseudo-random addresses, so it may just be you have an older
default setting. It doesn't really matter, unless you are worried by
the privacy implications of somebody knowing your MAC address.
 
> What happens with the duplicate address detection? The SLAAC one tries
> again, and my static one stays put?

Yes. This is a design feature of SLAAC. But in a 64 bit space, the
collision risk is remarkably low.

    Brian

> 
>>> Is there a more formal approach? Is this (SLAAC plus statics where
>>> required) the normal way of doing things?
>>
>> I think so, except for True Believers in DHCPv6, or people who pay good
>> money for APAM software.
> 
> Great, thanks a lot :-)
> 
> Richard
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