Re: New Version Notification for draft-halpern-6man-nd-pre-resolve-addr-00.txt

[Mark ZZZ Smith <[e-mail]>]

----- Original Message -----
> From: Greg Daley <[e-mail]>
> To: 'Ing-Wher Chen' <[e-mail]>; "[e-mail]" <[e-mail]>
> Cc: 
> Sent: Friday, 17 January 2014 1:14 PM
> Subject: RE: New Version Notification for draft-halpern-6man-nd-pre-resolve-addr-00.txt
> 
> Hi Helen,
> 
<snip>

> 
> 3/ Monitor the solicited nodes' addresses in the MLD querier router, and do 
> not transmit an NS from off-link for an incomplete address unless someone is 
> listening.
>

So I've been thinking for the last few months that this method could be a useful further mitigation to off-link ND cache attacks for routers. I've been writing something up which I've been planning to finish and post in the next week or so.

I think it could be fairly effective - there are a total possible 2^24 solicited-node multicast groups on a link, where as there will only be as many present ones as there are IIDs with unique lower 24 bits. For most subnets I think that will number in the order of 10s or 100s, and perhaps on rare occasions in the low 1000s. So NSes would only be necessary for e.g. 1000/2^24 portion of the unicast address space, otherwise the packets that would trigger them can be dropped (or perhaps sent to an RFC6018 greynet collector).

A neighbor cache attack is likely to be still be possible for the 2^40 portions of unicast address space covered by each of the the present solicited-multicast groups, however Fernando's Stable/Opaque IID draft would make them harder to find, even though it will increase the number of them, as there is an unique Opaque IID per prefix.

All routers listening to MLD track group membership, not just the MLD querier, so all routers on the link could implement this method.

Regards,
Mark.