Subject: [savi] SAVI prefix enforcement

From: "Joel M. Halpern" <[email-masked]>
Date: Thu, 02 Sep 2010 10:34:13 -0400

After discussion, we added text in the SLAAC document about SAVI 
enforcing prefixes advertised with RA.
I recently saw an interesting archtiectural description.

The Routers send out RAs with no prefix on a regular basis.
In response to an RS, they send out a prefix in a unicast RA.
The multicast RAs continue to have no prefix.

This has a couple of implications, I think.
First, it would seem that we should call attention to the fact that the 
messages may not carry the same information, and that information once 
learned should be retained until timeout.
Second, this may complicate the case of device reset when not directly 
attached, and / or topology change.  In either of those two cases, we 
could have a leaf that has a correctly assigned prefix, but we won't 
know it.  Due to the way these things are done, an RS with an 
unspecified source will NOT solve this, as it will not prompt an RA with 
the proper prefix.

Yours,
Joel

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From: marcelo bagnulo braun <[email-masked]>
Date: Thu, 02 Sep 2010 16:47:50 +0200

El 02/09/10 16:34, Joel M. Halpern escribió:
> First, it would seem that we should call attention to the fact that 
> the messages may not carry the same information, and that information 
> once learned should be retained until timeout.
Right, i think the SAVI device should send a RS and remember the prefix 
during its lifetime. also before removing the prefix it should try to 
renew it by sending a new RS:

> unspecified source will NOT solve this, as it will not prompt an RA 
> with the proper prefix.
i don't understand this, could you expand? I mean, i understand that an 
RS with the unspecifed source address will still trigger the RA with a 
prefix, right?

regards, marcelo

>
> Yours,
> Joel
> _______________________________________________
> savi mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/savi
>

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From: "Joel M. Halpern" <[email-masked]>
Date: Thu, 02 Sep 2010 10:56:50 -0400

As specified, the router needs the source information in order to decide 
what prefix to send in the unicast RA.  That is why it is unicast.

Now, it may be that the "source" is specified in some other field, which 
the SAVI device can provide, or which some device between the SAVI 
device and the router will fill in.  But it may require a more complex 
masquerade than merely an unspecified source.

Yes, it is an ugly architecture.

Yours,
Joel

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From: marcelo bagnulo braun <[email-masked]>
Date: Thu, 02 Sep 2010 17:28:25 +0200

El 02/09/10 16:56, Joel M. Halpern escribió:
> As specified, the router needs the source information in order to 
> decide what prefix to send in the unicast RA.  That is why it is unicast.

mmm, but how this works with the stateless address autoconf? (not with 
SAVI, but in general, i mean).
A node doing slaac will send the RS with the link local address, will 
the router send different prefixes depending on which link local address 
is contained as source address? Does this assumes a kind of ACL?

In any case, i think that learning the prefix through RA is an 
additional feature, which may not work in some configurations, such this 
one, and in that cas,e the prefixes need to be configured in the SAVI 
devices manually (along withthe list of which prefix send to which link 
local address)

But maybe i am missing somehting

Regards, marcelo

>
> Now, it may be that the "source" is specified in some other field, 
> which the SAVI device can provide, or which some device between the 
> SAVI device and the router will fill in.  But it may require a more 
> complex masquerade than merely an unspecified source.
>
>>> the messages may not carry the same information, and that 
>>> information once learned should be retained until timeout.
>> Right, i think the SAVI device should send a RS and remember the 
>> prefix during its lifetime. also before removing the prefix it should 
>> try to renew it by sending a new RS:
>>
>>> Second, this may complicate the case of device reset when not 
>>> directly attached, and / or topology change.  In either of those two 
>>> cases, we could have a leaf that has a correctly assigned prefix, 
>>> but we won't know it.  Due to the way these things are done, an RS 
>>> with an unspecified source will NOT solve this, as it will not 
>>> prompt an RA with the proper prefix.
>> i don't understand this, could you expand? I mean, i understand that 
>> an RS with the unspecifed source address will still trigger the RA 
>> with a prefix, right?
>>
>> regards, marcelo
>>
>>
>>>
>>> Yours,
>>> Joel

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From: "Joel M. Halpern" <[email-masked]>
Date: Thu, 02 Sep 2010 11:34:04 -0400

The main thing we need to do is put in just a few sentence about how to 
nadle inconsistent RA prefix information.

The case I am referring to is quite ugly, and relies on other devices 
adding extra information.  Unfortunately, as the architecture is still 
undergoing development, specifying more than just the need to handle 
inconsistent prefixes probably can't be done.

Yours,
Joel