IPv6 RA vs DHCPv6 - The chosen one?

Tomas Podermanski tpoder at cis.vutbr.cz
Tue Dec 27 21:23:48 UTC 2011


On 12/23/11 7:48 AM, Ray Soucy wrote:
> On Thu, Dec 22, 2011 at 3:04 PM, Tomas Podermanski <tpoder at cis.vutbr.cz> wrote:
>> Well, then how many devices do you have in the network that uses IPv6?
> Good question, and I applaud you for wanting to verify that people
> talking about IPv6 have legitimate experience deploying it.
> I dug into the database I log all IPv6 traffic into.  We have 8,509
> active hosts using IPv6, that's in comparison to 35,229 on the IPv4
> side, so about 24% (mind you, this is only the LAN networks we manage,
> we provide IPv6 transit to other entities as the regional R&E
> network).
> At this point over 95% of IPv4 LAN networks have IPv6 available,
> wireless is still a challenge (which is a big part of the difference
> between the host numbers you see above).
> We participate in Google's trusted IPv6 program, so Google announces
> AAAA's to us for nearly all their services, so a significant amount of
> bandwidth is actually over IPv6.  I would say that Google does make up
> the majority of IPv6 traffic though; there isn't much else out there
> announcing AAAA's yet.
> We have always taken the approach that IPv6 isn't ready to be deployed
> if you can't do so while maintaining the same standards you have for
> IPv4 in the areas of manageability, security, availability, and
> stability.  And we literally spent a few years modifying internal
> systems (and implementing new ones) to support IPv6 before we started
> making it available. See
> http://reports.informationweek.com/abstract/19/2233/Network-Infrastructure/strategy-session-ipv6.html
>   for the case I've been making the last few years, or listen to me
> (and others) talking a little about it on Cisco's Higher Education
> webcast series http://www.cisco.com/web/strategy/education/us_education/webcasts.html

I've watched the webcast and I like it. It's very realistic approach and
I especially agree with opinion that deploying IPv6 means going into
many compromises. We have been faced with very similar (almost same)
troubles that you have been talking about.
>> Do you have implemented first hop  security? What will you do when some
>> user runs RA flood attack
> You can hear me talk a little about that in the Cisco webcast.  Right
> now we maintain a PACL on our switches that filter RA or DHCPv6 server
> traffic originating from access ports.  As you mentioned it doesn't
> protect against malicious attempts to disrupt services on the network
> (fragmented packets) but it does add a reasonable level of stability
> (e.g. prevent Windows ICS) to levels that are similar to IPv4.  In
> addition, we have a process that monitors our routers for new RAs on
> the network, and alerts us to that (which would let us respond to a
> malicious RA that got past the PACL).

We are doing things just in the same way. Using PACL where is it
possible (almost nowhere) and rest of the network we are trying to
monitor. In case when an invalid RA appears we tries to repair it. For
that we use combination of scapy sripts and home made tools (we were not
satisfied with ndpmon, rafixd, ...).  My colleague had a talk at that
topic that is available
http://openwiki.uninett.no/_media/geantcampus:2011-gn3na3t4-ipv6-gregr.pdf .

Having over 120 subnets monitoring is not the perfect solution. Requires
installation of extra probes into each segment (so we do it only for
some segments) and can't solve malicious attacks. But is better than
nothing - for many subnets it is the only thing we can do. At least it
minimizes impact of Microsoft's ICS behavior.

We probably haven't see any malicious attack on that. It's quite
difficult say it for sure, because is quite difficult to distinguish
which RA's are originated on ICS or witch ones are "other" activity. But
remains that monitoring of rogue RA shows to us sometimes a really weird

I believe that is a matter of time when viruses/trojans will start using
IPv6 features to perform DNS hijack as we were able to observe it in
IPv4 (DNSChanger) a few years ago. Fortunately from a user perspective
there is still quite easy solution how to guard against that attack in
the IPv6 environment. I think we all know that solution :-)

> For neighbor table exhaustion, I've written a set of scripts that I
> can use in a lab environment to perform the attacks against the
> platforms we use, and test how they fair.  There is a pretty wide
> range of results.  Most of the larger platforms that are the ones we
> would be concerned about actually hit CPU limitations before neighbor
> table exhaustion is accomplished, mainly because the neighbor
> discovery process doesn't appear to be implemented in hardware.  It
> doesn't take much to pull off the attack either; a handful of
> residential connections would do the trick.  This isn't an IPv6
> problem so much as a vendor implementation problem, though.  Like most
> DoS and DDoS attack vectors, vendors will need to take extra steps to
> harden equipment against these attack vectors as they become aware of
> them.
> Until vendors catch up (and that includes us having the funds to
> upgrade to new platforms that do a better job with it), we have opt'd
> to make use of longer prefixes than 64-bit (in fact we mirror the
> capacity of the IPv4 prefix; so a /24 in IPv4 would be a /120 in
> IPv6).  A good description of this is available in some slides by Jeff
> Wheeler at http://inconcepts.biz/~jsw/IPv6_NDP_Exhaustion.pdf
> While your mileage may vary with longer prefixes, with the same
> attacks we saw the impact on CPU usage to be less than half when
> longer prefixes were used, and that's pretty good.  You can also keep
> external attacks from reaching internal routers if you don't do route
> summarization internally, which sees considerable gains, as more of
> that logic appears to be in hardware.

In that area we also tried to use longer prefixes than /64, but we had
difficulties on some devices. There was two kind of problems. Some of
devices weren't able properly handle longer prefixes for example in
routing protocols. The second group of devices tries to solve processing
longer prefixes via software. So we had to gave up of using longer
prefixes and now we uses 64-bit prefixes including point to point links
(and hope that nothing will happen). But fact is that was 3 years ago,
so maybe today the situation is much better. I haven't check for long time.

> On the deployment side, we make use of DHCPv6 and RA with M and O set,
> and A unset.  Our DHCPv6 servers only hand out IPv6 addresses to
> registered systems that are in the database and have been flagged as
> OK for IPv6.  This has allowed us to roll out IPv6 on a host-by-host
> basis, rather than a network-wide basis (as you would need to do with
> This does have the consequence of excluding hosts from IPv6,
> piticurally Windows XP systems, and pre-Lion OS X systems.  But since
> IPv6 isn't "required" yet (there is really no IPv6-only content yet),
> we take the position that we only provide IPv6 to systems that support
> DHCPv6 and have an adequate IPv6 host-level firewall as part of their
> IPv6 implementation.  This makes it easy to exclude hosts that might
> be problematic to deliver IPv6 to, due to lack of security, or even
> bugs (RHEL 3 can kernel panic when connected to over IPv6, for
> example).  It also keeps the pressure on to upgrade legacy systems.

With that we had a little differed attitude. Our idea was preferring
native connectivity instead of running unattended tunneled traffic and
traffic forwarded by ICS. We also were not certain whether SLAAC or
DHCPv6 would be widely used. So we decided to preffer SLAAC because we
wanted support as much system as possible. We also tried to develop our
system solving data retention with connection to privacy extension 
(tech report http://www.fit.vutbr.cz/research/view_pub.php?id=9840 and
related presentation
. It runs quite well in our campus, it is maybye interesting research
project but frankly said I have doubt whether such system is reliable to
use in really large scale. 

Now, when apple started supporting DHCPv6 it seems to me that DHCPv6
will be a common way for configuring addresses in a enterprise
environment so maybe we will start thinking about it. There is another
big issue with DUIDs.

Talking aboud DUIDs how do you solve that problem in your environment ?
For v4 we have automatized (home made) system where users register their
MAC addresses and based on it the the configuration for DHCP servers is
created. In your presentation I saw that something similar is used in
your environment as well. Do you use some automatized system for
gathering UIDs or do you have to manually maintain a new DUID after
every re-installation of OS ?

> Wireless is an area we would really like to move forward with IPv6,
> but we still have concerns that need to be addressed before that can
> happen.  In a Cisco environment, like ours, for example.  IPv6
> requires Ethernet Mode Multicast to be enabled on the WLAN.
> Unfortunately it doesn't provide tools to filter which multicast
> traffic is permitted, and at the scale we deploy wireless it just
> isn't practical.  We might be able to re-architect wireless to better
> handle this, but that's a future project.
> I think the big picture here is that IPv6 isn't as "easy" as it should
> be for large deployments just yet, but that's the case with any new
> technology.  The more people who begin to work through it, the more we
> will identify problems, and work to resolve them.

I agree with you. Deploying IPv6 is really not easy and not cheep as
some IPv6 enthusiasts claims. Having practical experience it seems to me
that many things in IPv6 that are very differed comparing to IPv4 (and I
am not sure whether all this differences are really necessary) and that
is the reason why many people and organizations prefer putting off
deploying IPv6 instead investing effort and - of course - money.


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