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Anybody can participate in the IETF (Was: Why is IPv6 broken?)



On Mon, Jul 11, 2011 at 7:48 PM, Jimmy Hess <mysidia at gmail.com> wrote:
> If every vendor's implementation is vulnerable to a NDP Exhaustion
> vulnerability,
> how come the behavior of specific routers has not been documented specifically?

Well, I am in the business of knowing the behavior of kit being
considered by my clients for their applications.  Every box breaks
when tested, period.  I imagine you have tested zero, thus you have no
data of your own to go on.  No vendors are rushing to spend money on
"independent" testing laboratories to produce reports about this,
because they pretty much all know their boxes will break (or are not
even aware of the potential problem, in the case of a few scary
vendors.)

> If ?"zero" devices are not vulnerable, you came to this conclusion
> because you tested
> every single implementation against IPv6 NDP DoS, ?or?

Although I have tested many routers to verify my thinking, if you
actually read the slides and understand how routers work, you too will
know that every router is vulnerable.  If you don't know, you don't
understand how routers work.  It's that simple.

> How come there are no security advisories.
> What's the CWE or CVE number for this vulnerability?

Again, no one is interested in this problem yet because vendors really
don't want their customers to demand more knobs.  Cisco is the only
vendor who has done anything at all.  If you read about their knob,
you immediately realize that it is a knob to control the failure mode
of the box, not to "fix" anything.  Why?  It can't be "fixed" without
not using /64 (or similar) or going to the extreme lengths I outline
in those slides.

> It would be useful to at least have the risk properly described, in
> terms of what
> kind of DoS condition could arise on specific implementations.

Let's take 6500/SUP720 for example.  On this platform, a policer is
shared between the need to resolve ARP entries and ND table entries.
If you attack a dual-stack SUP720 box it will break not only IPv6
neighbor resolution, but also IPv4 neighbor resolution.  This is
pretty much the "worst-case scenario" because not only will your IPv6
break, which may annoy customers but not be a disaster; it will also
break mission-critical IPv4.  That's bad.  Routing-protocol
adjacencies can be affected, disabling not just some hosts downstream
of the box, but also its upstream connectivity.  It doesn't get any
worse than that.

You are right to question my statements.  I'm not an independent lab
doing professional tests and showing the environment and conditions of
how you can reproduce the results.  I'm just a guy helping my clients
decide what kit to buy, and how they should configure their networks.
The only reason I have bothered to produce slides is because we are at
a point where we have end-customers questioning our reluctance to
provision /64 networks for mixed-use data-center LANs, and until
vendors actually do something to address this, or "the standard"
changes, I need to increase awareness of this problem so I am not
forced to deploy a broken design on my own networks the way a lot of
other clueless people are.

Again, this is only hard to understand (or accept) if you don't know
how your routers work.
* why do you think there is an ARP and ND table?
* why do you think there are policers to protect the CPU from
excessive ARP/ND punts or traffic?
* do you even know the limit of your boxes' ARP / ND tables?  Do you
realize that limit is a tiny fraction of one /64?
* do you understand what happens when your ARP/ND policers are reached?
* did you think about the impact on neighboring routers and protocol
next-hops, not just servers?
* did you every try to deploy a /16 on a flat LAN with a lot of hosts
and see what happens?  Doesn't work too well.  A v6 /64 is 281
trillion times bigger than a v4 /16.  There's no big leap of logic
here as to why one rogue machine could break your LAN.

There is no router which is not vulnerable to this.  If you don't
believe me, read the Cisco documentation on their knob limiting ND
entries per interface, after which there may be service impact on that
interface.  That's the best anyone is doing right now.  Of course,
vendors understand that we, as customers, can configure a subnet
smaller than /64.  They are leaving us open to link-local issues right
now even with a smaller global subnet size, but at least that cannot
be exploited from "the Internet."  And as it happens, exactly the same
features / knobs are needed to "fix" both problems with /64, and with
link-local neighbor learning.

-- 
Jeff S Wheeler <jsw at inconcepts.biz>
Sr Network Operator? /? Innovative Network Concepts