Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds

Fernando Gont <fgont@si6networks.com> Thu, 31 October 2019 19:44 UTC

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To: Owen DeLong <owen@delong.com>, Ted Lemon <mellon@fugue.com>
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From: Fernando Gont <fgont@si6networks.com>
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Date: Thu, 31 Oct 2019 16:43:08 -0300
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Subject: Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds
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On 27/10/19 16:35, Owen DeLong wrote:
> 
> 
>> On Oct 27, 2019, at 10:14 , Ted Lemon <mellon@fugue.com
>> <mailto:mellon@fugue.com>> wrote:
>>
>> On Oct 27, 2019, at 11:05 AM, Philip Homburg
>> <pch-v6ops-9@u-1.phicoh.com <mailto:pch-v6ops-9@u-1.phicoh.com>> wrote:
>>> If you think that this is an important thing to fix, feel free to 
>>> talk about it. But why in this discussion? SEND doesn't do anything for
>>> flash renumbering. From an operational point of view, RA-guard is much
>>> more attractive then SEND. So it is not clear to me that there is any
>>> need for SEND. But I could be wrong. In any case, if there is a need
>>> to discuss SEND we could do that separately.
>>
>> I think you missed my point.  You can’t do flash renumbering by
>> advertising a prefix with a valid lifetime of zero, because that will
>> be ignored by hosts.   If it were not ignored by hosts, it would be a
>> very effective DoS vector.    And so if you want to be able to flash
>> deprecate a route, you need some way to validate that the deprecation
>> is coming from the same source as the route.   Hence my suggested
>> “limited SEND”.
>>
>> Limited SEND would not be hard to implement.   Yes, it would be
>> marginally harder than just saying that hosts should accept flash
>> deprecation of prefixes.   But nobody with any sense is going to
>> implement that in their IP stack, so in practice if you want this to
>> work, you need some way to do flash deprecations that doesn’t create a
>> massive attack vector.
> 
> It’s only a DOS vector if the attacker is already on-LAN.
> 
> I recognize that there are environments where that is expected behavior
> (e.g. Coffee Shop Wifi, University networks, etc.),but
> it’s not the case for the average residential CPE and residential LAN
> segments.
> 
> In the vast majority of situations where I would expect hostile hosts to
> be likely to be on LAN, I don’t think I’d be using
> SLAAC for address assignment in the first place. Most likely, I’d want
> stateful DHCP in such instances.

You can do SLAAC as long as you do FHS. At which point the issue raised
by Ted is a non-issue.


-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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