On 2012-03-20 21:51, Anders Brandt wrote:
> Kerry Lynn writes:
>
>> On Sat, Mar 17, 2012 at 2:22 AM, Dave Thaler <[email protected]>
>> wrote:
>>> Brian Carpenter writes:
>>> [...]
>>>> Let me be clear. If a local service has (for some reason) both a ULA
>>>> and a non- ULA global address, and the host has both, I think the
>>>> correct default behaviour is for the ULA address pair to be used.
>>> As I put into the doc, I don't think that's quite right.
>>>
>>> If both the source and dest ULAs are in the same /48 then I think the
>>> correct default is as you say (use ULA).
>>>
>>> If the source and dest ULAs are in different /48's then I think the
>>> correct default is instead to use the non-ULA global, since there's no
>>> guarantee of routability between different /48s. So unless configured
>>> otherwise, one has to assume it's far more problematic than a non-ULA
>> global.
>> Do you mean "no guarantee of symmetric routability"? The fact that the
>> packet arrived in the first place seems to indicate earlier policy choices
>> (e.g.
>> the sender may not have a non-ULA global address, and the two /48s already
>> seem to share a common definition of "site").
>>
>> I am still relatively new to homenet and I am surely missing a lot of
>> background. Has anyone discussed dealing with multiple /48 ULA prefixes
>> in a single site?
>
> I would like to second Kerry.
>
> It is a surprise to me that ULA addresses are not by default routable within
> the site.
> I can easily imagine a number of LLN border routers which autonomously
> allocate
> different ULA prefixes for use within their individual LLN subnets.
IMHO that should be a NOT RECOMMENDED behaviour. ULAs make sense if they
cover an entire enterprise or home network, but not if they cover a subset.
> Meeting a ULA address outside the local prefix will cause the LLN node to
> forward
> its IP packets to the default gateway (border router) of the LLN subnet. This
> way
> packets can travel between LLN subnets using normal routing with long-term
> stable
> ULA addresses. We need the stable addresses for control-style applications in
> LLNs.
>
> Obviously it requires a routing protocol in the (homenet) LAN but are there
> other issues?
It doesn't just require a routing protocol; it also requires a routing policy
that knows which routers have to block the ULAs (plural). That seems a lot
more complex that a rule that says only a border router originates and delegates
a ULA prefix, because that border router would also know to block the
prefix across the border.
Anyway - maybe you should look at draft-liu-v6ops-ula-usage-analysis
and discuss it over on v6ops.
Brian
>
> Thanks,
> Anders
>>> You'll find the above logic in the current 3484bis draft.
>>>
>>> -Dave
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