IPv6 prefixes longer then /64: are they possible in DOCSIS networks?

Tue Nov 29 07:20:44 UTC 2011

On Mon, Nov 28, 2011 at 10:43 PM, <Valdis.Kletnieks at vt.edu> wrote:

> On Tue, 29 Nov 2011 00:15:02 EST, Jeff Wheeler said:
>
> > Owen and I have discussed this in great detail off-list.  Nearly every
> > time this topic comes up, he posts in public that neighbor table
> > exhaustion is a non-issue.  I thought I'd mention that his plan for
> > handling neighbor table attacks against his networks is whack-a-mole.
> > That's right, wait for customer services to break, then have NOC guys
> > attempt to clear tables, filter traffic, or disable services; and
> > repeat that if the attacker is determined or going after his network
> > rather than one of his downstream customers.
>
> It's worked for us since 1997.  We've had bigger problems with IPv4 worms
> that
> decided to probe in multicast address space for their next target, causing
> CPU
> exhaustion on routers as they try to set up zillions of multicast groups.
>
> Sure, it's a consideration.  But how many sites are *actually* getting hit
> with this, compared to all the *other* DDOS stuff that's going on?  I'm
> willing
> to bet a large pizza with everything but anchovies that out in the *real*
> world, 50-75 times as many (if not more) sites are getting hit with IPv4
> DDoS attacks that they weren't prepared for than are seeing this one
> particular neighbor table exhaustion attack.
>
> Any of the guys with actual DDoS numbers want to weigh in?
>

Agreed. While I don't have any good numbers that I can publicly offer up,
it also intuitively makes sense that there's a greater proportion of IPv4
DDOS and resource exhaustion attacks vs IPv6 ones.
Especially on the "distributed" part; there's a heck of lot more v4-only
hosts to be 0wned and botnet'ed than dual-stacked ones.

That said, I think the risk of putting a /64 on a point-to-point link is
much greater than compared to a (incredibly wasteful) v4 /24 on a
point-to-point. Instead of ~254 IPs one can destinate traffic towards (to
cause a ARP neighbor discovery process), there's now ~18446744073709551614
addresses one can cause a router to start sending ICMPv6 messages for.

For links that will only ever be point-to-point, there's no good reason
(that I know of) to not use a /127. For peering LANs or places that have a
handful of routers, /112's are cute, but I would think the risk is then
comparable to a /64 (which has the added benefit of SLAAC).

I imagine the mitigation strategies are similar for both cases though: just
rate-limit how often your router will attempt neighbor discovery. Are there
other methods?

Cheers,
jof