IPv6 Security & Capability Testing, Part 2

In this post I want to give an overview of IPv6 security testing efforts performed by various researchers in the past. As laid out in the first part of this series such testing can be considered one of the pillars of an overall IPv6 security strategy in complex environments. I will also try to develop a bit of a classification approach as for the ‘questions’ that the individual testing efforts were supposed to answer.

One of the earliest efforts was undoubtedly Marc Heuse‘s PacSec 2005 talk on “Attacking the IPv6 Protocol Suite” in which he discussed the now famous THC IPv6 toolkit for the 1st time in public. That talk was mainly focused on general IPv6 properties and how to exploit them. Another milestone of IPv6 security research (albeit quite a few years later than Marc’s talk) was Antonios Atlasis‘ Black Hat EU 2012 talk on “Attacking IPv6 Implementation Using Fragmentation“. I saw that one live as I presented at the same event myself, and I remember being impressed by the huge security impact that seemingly small implementation nuances can have (e.g. CVE-2012-4444 in the Linux kernel was one outcome of that research). I also realized that IPv6 fragmentation can be a really bad thing from a security perspective. That work was heavily focused on the ‘how do different implementations behave [when confronted with specific packets], and why does it matter’ angle. Highlighting that differences between IPv6 stacks exist, and that these might be relevant for an implementation’s security posture, was an important contribution/message in itself.
Antonios then expanded his research into looking at the way how various firewalls handled IPv6 fragmentation and IPv6 extension headers (2013, together with Christopher “Chris” Werny), and how IDPS systems could be evaded by means of extension headers (2014. see also the “Hiding in Complexity” talk by Marc Heuse in 2015). Similar testing was done by Marc & Fernando Gont (“Security Assessments of IPv6 Networks and Firewalls“, 2013) and by Johannes Weber in his master thesis (“IPv6 Security Test Laboratory”, 2013). All these research efforts explicitly looked at both IPv6 implementation differences on security components and at their resilience when being exposed to individual (and potentially ‘peculiar’) IPv6 packets. At the time another group of researchers performed various related activities at the University of Potsdam (see also their publications); a few results of their work were presented at the Troopers IPv6 Security Summit 2014.

Some of the above papers included (more or less detailed) descriptions of test cases, but the most comprehensive taxonomy of tests to be performed with regard to the secure implementation of IPv6 on operating systems or network devices could be found in the “Testing the security of IPv6 implementations” paper published in March 2014 by a group of (mostly) Dutch researchers (incl. Cristofaro Mune and Albert Spruyt):

Since then not much has happened in the space of IPv6 security research centered around implementation differences of OSs or network devices (I myself contributed to lab testing of various OSs in the context of SLAAC/DHCPv6, IPv6 source address selection or RFC 6980 support, although besides the latter none of these had a specific security perspective). A notable exception is a Ph.D. thesis on “Measuring IPv6 Resilience and Security” published in 2019, but they mostly looked at the real-life distribution of specific patterns and IPv6 security issues on an Internet scale (as opposed to performing tests in one individual environment and/or in a lab). While this is super-interesting research it is supposed to answer a different (set of) research question(s). Also there is an interesting paper/thesis on “IPv6 Security Issues in Linux and FreeBSD Kernels: A 20-Year Retrospective” from 2018 (authored by Jack Cardwell, with my old friend Sergey Bratus as advisor).
On the other hand I can confirm from IPv6-focused security assessments in customer environments which Chris and I led between 2016 and early 2019 that significant implementation differences still exist(ed) in more recent times. Maybe it’s hence time to revive such testing efforts, now that IPv6 deployment gains ever more traction in enterprise environments? In another post I will discuss how a framework for testing IPv6 implementations from different (not only security-centric) perspectives could look like.

Stay tuned, and thank you for reading so far ;-).

IPv6 Security & Capability Testing, Part 1

Let’s be realistic about this: the advent of any new technology in a complex IT environment can lead to additional vulnerability exposure and hence to additional risk. Given the fundamental role of IP for practically all communication acts and all digital services in today’s organizations this is particularly true for IPv6.

On the other hand as an IPv6 practitioner one definitely wants to avoid being responsible for significantly increasing the risk exposure of an environment, not least as it’s already hard in itself to drive the deployment of a protocol which shines by a lot of added – and, maybe, from today’s 20/20 perspective: unnecessary – complexity while at the same time, rightfully or not, being perceived as bringing just one single advantage, that is larger address space.

This is why I want to discuss in a small series of posts some thoughts how to deal with this situation. What are the things to keep in mind or to focus on, when IPv6 is gaining traction in any sufficiently large, complex and heterogeneous environment?

Said additional exposure can stem from several factors:

  • Lack of operational experience (we as the IPv6 community can try to contribute to curing this by training & education, but of course there will be gaps for some time/years). These two papers (both from 2016) lay out some differences between IPv4 and IPv6 from an Internet scanning perspective, and quite some of those observed differences could be attributed to disparities in operational practices.
  • Lack of available security mechanisms & processes. I’m not the biggest fan of the ‘let’s just transfer our security architecture & technologies from the IPv4 world to IPv6’ approach, but it’s a commonly found and – considering the often significant efforts of deploying IPv6 – fully legitimate approach (I mean we as IPv6 practitioners shouldn’t expect our valued peers from the security groups to heavily re-engineer their stuff just because of our new thing, and I’m fully serious here). On the other hand it might just be that such a ‘simply transfer’ strategy can’t be pursued due to hardware limitations (TCAM memory comes to mind) or due to performance penalties arising from IPv6. While from 2013, this diagram (from a presentation at the ‘IPv6 Hackers’ meeting at IETF 87) might give an idea of the latter:
  • Specifics of the new technology in question. In case of IPv6 this might encompass factors like new protocol features with possible security impact (router advertisements or MLD come to mind), the generally huge variety when it comes to IPv6 stacks & their properties, and finally the potential immaturity of those stacks. I mean in 2020 we shouldn’t see things like this or this anymore, right?

This last aspect is the reason why I think that the following three elements should be part of the security side of each IPv6 deployment in a complex environment:

  • Make sure that any IPv6-enabled system is properly protected by (at least) some packet filtering mechanism (be it an ACL on the network layer or a host-based component) from the very beginning. This is particularly important as you should always assume global reachability due to IPv6 GUAs and due to the potential lack of control your security groups might have over route announcements and route filtering. How to audit this (existence of packet filter on some layer for all systems) can be an interesting challenge, and I might get back to this at a later point/post.
  • Make sure that all IPv6-enabled systems are covered by your organization’s vulnerability scanning process in case such a thing exists. Given one can not reasonably scan IPv6 subnets sequentially this might actually require some changes to said process.
  • Create transparency with regard to the capabilities & properties of individual IPv6 stacks to be found in the organization, e.g. when it comes to RFC 6980 support or to their susceptibility as for malformed IPv6 packets.

The actual vulnerability exposure and the associated risk level of your IPv6 deployment will highly depend on these three factors. In the next post I will particularly focus on the third of those, that is on ideas and approaches how to create such transparency.

Stay tuned, and thanks for reading so far.

Does One Need DHCP(v6)?

I’ve covered DHCPv6 quite a bit in the past, e.g. in these two ‘A Deep Dive into DHCPv6’ blogposts, this one on RFC 6939, a few other contributions discussing it in some way (1, 2, 3) and a talk on ‘Secure & Reliable DHCPv6’ at the Troopers #TR15 IPv6 Security Summit (slides & video).

I also had a number of Twitter exchanges on DHCPv6, and one of the communication partners recently reached out to me with an interesting question. That person asked: “we consider avoiding DHCPv6 in our campus networks, but the security team insists on using it to be able to properly identify systems which act in a malicious way. what’s your opinion?” – In this post I’ll try to give a response.

Before I start with a technical discussion myself let me further add that several IPv6 deployment case studies mention all types of issues with DHCPv6, like this one from CERN, this one from Microsoft and this one from Deutsche Telekom. You might think about this for a second… (if this wasn’t clear, let me rephrase: in general DHCPv6 might be a piece of crap whose use should be carefully considered from a production [-readiness] perspective).

In ancient IPv4 times, in enterprise networks usually DHCP served one or several of the following functions:

  • 1a) provisioning of dynamic addresses (in a more or less centralized manner).
  • 1b) provisioning of other IP-related parameters/properties needed by clients (default gateway, DNS resolvers, NTP servers, others e.g. place to find firmware/boot image etc.)
  • 2) simple access control (like ‘only MAC addresses registered in CMDB get an IP address from DHCP’, which is supposed to prevent unauthorized network access. I’ve once seen this in a large automotive ICS environment).
  • 3) contribute to DFIR activities by providing mapping of MAC addresses to IP addresses found in log files, PCAPs etc.

Now let’s look at those from an IPv6 perspective.

  • 1) For address provisioning DHCPv6 is no longer needed (hosts can do that on their own, via SLAAC), for the default gateway it can’t be used, and the vast majority of systems can get their DNS resolvers via RAs (option 25/RDNSS as of RFC 8106; see also Chrispost when Windows 10 eventually had it). That leaves distributing NTP servers which in turn some operating systems take into their own hands anyway (e.g. Windows).
  • 2) That ‘simple access control’ approach could be considered a curiosity for specific environments, and some of you might be reminded of those times when a printer’s test page (containing a MAC address) was sufficient to get access to enterprise networks running complex & expensive ‘NAC’ solutions…

That leaves us with the ‘we need DHCP(v6) for DFIR contributions’ thing, which was at the core of the initial question. To evaluate (the need for) this we should keep in mind that during a host’s lifecycle on a network a lot of properties can potentially be observed at various points. These include

  • the MAC address(es)
  • IPv6 address(es)
  • IPv4 address(es)
  • FQDN
  • mDNS-related information or similar (NetBIOS names)
  • username, e.g. in authentication context
  • X.509 certs (machine-/user-based) and namely the wealth of data they contain
  • RADIUS-related information

The correlation of the first two ones (MAC address to IPv6 addresses) or, maybe even better, to a username might hence be easily inferable from other information which is observable/can-be-logged at some point of a host’s lifecycle, e.g. X.509 cert based info in the context of Wireless EAP protocol (EAP-TLS or PEAP in most enterprise networks).
Read: you might not need DHCPv6 logs for that but just have a look at other sources available anyway (Bryan ‘The Packet Master’ Fite once coined the term ‘latent capabilities’ for this approach). In the following I’ll provide some examples.

Probably the best known of such capabilities is the ‘ipv6 neighbor binding logging’ command from Cisco’s IP Snooping framework which is available on most of their (physical) enterprise level switches (please note that I’ve never been a big fan of most features of that tool set, due to it’s complexity and immaturity in [test] deployments I’ve seen, but that logging capability is definitely helpful).

Another example would be the ‘NDP Monitoring‘ feature on Palo Alto devices which I learned about from Johannes Weber:

Finally here’s a very nice example which my friend Eric Vyncke showed in his session on IPv6 security at last year’s Cisco Live Europe:

tl;dr: instead of using DHCPv6 (bringing its own complexities and troubles) to solve that security requirement it might be a much better idea to analyze which data bits one might have available in an environment anyway and how to correlate them.
Assuming that some of you readers are still in the early stages of the IPv6 deployment in your organization you might even be able to file respective feature requests (e.g. ‘logging of IPv6 address(es) and MAC address of a client directly after its association in a wireless network’) to the vendor of your network gear.


I attended the OARC 32 in San Francisco workshop today and in this post I’ll provide some notes on talks I found particularly interesting. For those interested the full agenda can be found here and some information on the DNS-OARC organization themselves here.

Brian Somers: Recursive Resolution from the ground up
This was a super-interesting talk from Brian Somers, Cisco, in which he laid out how they implemented DNSSEC in OpenDNS. He discussed the – various – challenges they faced on that journey, together with some design decisions. Initially they had planned to support fragmented responses which, in hindsight, he called a ‘huge debacle’, for reasons shown on this slide (regular readers might have an idea why I mention this ;-):

This one gives an idea of the inherent complexity of their undertaking (well, more correctly: of the complexity of DNSSEC…):

Furthermore he mentioned that they only saw a 10% increase of network traffic after setting the DO (‘DNSSEC OK’ => ‘willing to get signed responses’) flag, and that they didn’t notice a significant CPU penalty (but they had performed some optimizations in the course of the project, plus hardware upgrades).
Paul Vixie gave a related lightning talk (PPT slides here) on the “Avoid IP fragmentation in DNSInternet-Draft in the afternoon, out of which one might find this slide particularly interesting:

Slides of Brian Somers talk here (PPT).
Video here (starts 17:30).
Slides of their DEF CON 27 talk on DNS poisoning attacks based on fragmentation here.
Some notes on DNS flag day 2020 plus links to the relevant research papers in this post.

Edward Lewis: The Different Ways of Minimizing ANY
RFC 8482 discusses potential approaches how DNS servers can react to queries of the ‘ANY’ type. Measurements performed by Edward show that different servers respond in many different flavors:

which in turn raises several questions/concerns:

Again, regular readers know I have a certain stance on protocol complexity – as an IPv6 person I heavily suffer from it on a daily basis ;-), see also this post and my RIPE 74 presentation on IPv6 security aspects. I hence very much liked this part of Edward’s talk

Overall a quite refreshing presentation, and I always have a sympathy for talks with real-life data.
Slides here.
Video here (starts at 52:50)

Ralf Weber & Mark Dokter (both Akamai): DNS Encryption Operational Experience and Insights
Another good talk with real-life measurements, this time on the behavior of different DoH/DoT clients. Two quick points on this one: first, having done some work in the space of X.509 certificate infrastructures in an ancient stage of life, I’m a bit worried when looking at this 😉

Secondly I found their notes on tuning the stack/kernel of the lab servers (quicker re-use of ports and increase of filehandles, as every connection needs one) quite interesting:

Slides here.
Video here (starts 34:30).

Dan Mahoney (from ISC): F-Root Updates
Yet another real-life case-study talk – lovely! ;-). Dan discussed challenges, design decisions and choices of hardware & software during their recent upgrade of the F-Root. While one might think that ‘the F-Root’ is mainly about DNS-related components, in reality many pieces are involved like network hardware and routing daemons:

Very solid talk, with quite some interesting technical insights!
Slides here.
Video here (starts 28:15).

While DNS is not my primary domain of work or expertise I really enjoyed the day incl. some good conversations during the breaks.

Wishing everybody a great Sunday, and those of you still in SFO have a good NANOG 78 meeting.

Organizational Security Implications of IPv6

In this post (with a very German, bulky title 😉) I’ll take a look at the implications of IPv6 on the security controls & processes in common enterprise environments, based on a few customer projects I performed in 2016–2019.

As I laid out in my presentation in the IPv6 WG at the RIPE79 meeting in Rotterdam there’s three main, say, ‘dimensions’ of (the advent) of IPv6 in an IT environment:

  • IP addresses identify entities (e.g. interfaces of systems) within networks, for a certain duration/amount of time (with IPv6 the latter plays a much more important role than in IPv4 networks, think ‘lifetime’). Here (the existence of) an IP address usually precedes the actual communication act – “I have an IP address, therefore I am [ready to communicate]”.
  • Certain systems can use the IP addresses of other systems to take specific actions, like routers performing forwarding decisions based on destination IP addresses of packets or firewalls dropping packets based on their addresses. The IP address is looked at during the act itself – “Show me the address(es) of a packet and let’s see what I’ll do with it”.
  • IP addresses can be processed (e.g. read from or written to files, put into databases or be analysed based on algorithms) by applications or system processes. Some of these types of operations are highly security-related, like in the context of incident response or fraud detection. This can happen in close temporal proximity (‘real-time’) or in retrospective. For this temporal dimension the above mentioned property of validity/lifetime has to be taken into account.

From an IPv6 deployment perspective namely the third above dimension is of great importance (and usually is the one leading to multi-year IPv6 programs) as the places/functions where IP addresses are processed usually constitute dependencies to be solved before the first two former dimensions can even be touched.
Configuring IPv6 rules on a firewall (2nd dimension) doesn’t make sense if the analysis framework/infrastructure isn’t capable of IPv6 (3rd dimension), and merely enabling IPv6 on systems (1st dimension) without having the capability to filter IPv6-related traffic (2nd dimension) can actually be quite dangerous.
That’s why, as some of you dear readers have painfully experienced, usually one has to start an IPv6 project with (taking care of) the 3rd dimension…

Now, to better understand the implications of IPv6 on security controls & processes, one approach could be to take a look at the NIST Cybersecurity Framework (which I also briefly discussed in my talk in the Troopers 2019 Defense Track) and to identify all (sub-) categories potentially affected by IPv6, in one of the above dimensions.

When doing so some generalizations can be observed.

In the context of the Identify function mainly three areas are affected:

  • Wherever IP addresses are used to contribute to a function (e.g. as an identifying property of an asset/a system), the underlying databases or -models might have to be adapted, in order to account for the different format of IPv6 addresses (128 bits instead of 32 bits, hexadecimal characters, different delimiter of parts of the address) and for the fact that usually multiple IPv6 addresses co-exist on individual interfaces (see also some of the points in this old post).
  • Evidently vulnerability management will be heavily affected in most organizations. Sequential scanning of subnets doesn’t work anymore, systems might expose different vulnerabilities over IPv6 than over IPv4 (see the sources mentioned in this thread) and link-local connectivity might play a role, too.
  • Finally there’s some sub-categories in the Identify function covering threats & risk management. Those have to consider IPv6, both wrt to IPv6-specific threats & risks (some of those were covered in my RIPE78 tutorial which is linked in the beginning of this post) and as for suppliers/the supply chain where IPv6 might also kick in.

Not too surprisingly IPv6 will also heavily affect controls & processes in the field of the Protect function:

  • Many technical controls used to protect assets will have to be reviewed as for their IPv6 capabilities, and their configuration (and maybe even the underlying architecture) might have to adapted for IPv6.
  • Audit & logging is one of the sub-categories in Protect (see PR.PT-1) and this is a classic example of the above 3rd dimension of IP addresses (‘being processed by a system process or an application’) which might require (potentially complex) adaptions for IPv6.

In a similar way several (sub-) categories of the Detect & Respond functions will be affected:

  • Detection, analysis and correlation methods might have to be modified/enhanced for IPv6.
  • IPv6-specific training of personnel performing tasks in the context of these functions will be needed.
  • Processes in the incident response and digital forensics context have to take different types of addresses, their intricacies (interfaces with multiple addresses of varying lifetimes) and the co-existence of different address families into account.

As you can see, quite a few security-relevant elements within an organization will have to be reviewed and adapted in the course of an IPv6 deployment effort. Transitioning to IPv6 is much more (complex) than just enabling IPv6 addresses on systems.
Challenge accepted, I’d say, given we don’t have any alternative to IPv6…

Happy to receive any type of feedback (Twitter is usually a good channel ;-).
You all have a great week,

A slide deck with some of these thoughts can be found here:

Some Notes on IPv6 Bogon Filtering

At first a happy new year to you all!
For some of us it will bring IPv6-related happiness (and maybe a few – although temporary 😉 – sorrows). The IPv6 world is full of sources of pain & heated discussions, but in today’s post I will discuss a topic where life got presumably easier with IPv6 than it was with IPv4, that is the filtering of inbound traffic at network borders, based on source addresses considered to be invalid with regard to the place (of filtering) and the direction of traffic. This is often called “bogon filtering” or “filtering of martians” (more details and terminology to follow in a second).

People do this for various reasons like

  • General/basic network hygiene (“obviously such packets are – at least when coming in over the Internet – somewhat invalid, so we don’t want to see them in our network”).
  • Potential protection from (D)DoS attacks using spoofed source addresses from such prefixes (e.g. based on random source addresses). There’s varying numbers & opinions as for the extent of those addresses within such attacks, so one might follow this line of reasoning or not (=> this debate is not in scope of this post).
  • Some regulatory frameworks might require such filtering, e.g. PCI DSS section 1.3.3 (as of v3.2.1) mandates for anti-spoofing filters.
  • It’s considered best practice in certain contexts (no judgement from my side implied here).

Frankly I’m not a super big fan of spending much energy on this as I don´t really see a reasonable cost (operational effort, in particular when not done properly) to benefit (risk mitigation) ratio here – I will happily swap a full bogon filter list for some solid filtering of IPv6 extension headers if I had to choose between the two 😜 – , but it’s a recurring topic in IPv6 security circles. In fact after my RIPE79 talk on (types of) IP addresses and their security implications a reader reached out to with a question along the lines: “so should we just filter all prefixes as of slide 23 of your deck?” (which essentially contained a screenshot of the “IANA IPv6 Special-Purpose Address Registry”). Let me hence take this as an opportunity to discuss some intricacies of address-based network ingress filtering.

Usually the related rules of such ACLs can be broken down to the following categories:

  • Drop “special use”/”special-purpose” prefixes which are not supposed to be seen in across-the-Internet production traffic, like the (majority of) addresses prefixes as of these lists for IPv4 and IPv6.
  • Drop packets originating from address ranges not (yet) allocated by IANA or the RIRs.
  • Anti-spoofing (drop packets at the network borders / ingress that pretend to originate from internal networks).
  • Others, e.g. filtering packets based on (presumed) country of origin (see for example this post by Koen van Impe).

Before we analyze an actual example I’d like to come up with a bit abstract classification (regular readers know I sometimes expose a tendency to over-intellectual abstractions 😉) of address ranges typically found in such lists, together with a discussion of their operational implications.
I suggest going with the following categories:

  • Special-purpose addresses that can usually be dropped without much consideration (=> default approach: include in list). The ‘documentation’ prefix 2001:db8::/32 (see RFC 3849) can serve as an example here – I can’t see any reason why one would accept packets with such a source address over the Internet.
  • Special-purpose addresses that shouldn’t be filtered in most cases (=> default approach: do not include). For example I generally recommend not touching link-local addresses on transit networks between routers as this might impact (namely the session establishment of) routing protocols.
  • Special-purpose addresses that need some consideration, based on an individual environment’s needs and objectives (no default, but “think about it”).
  • Unallocated space. Here the main thing to keep in mind is that this might change over time (e.g. the RIPE NCC just started de-bogonising 2a10::/12). So one might only include prefixes of this type if operational procedures and maturity allow to update in case changes occur in this space (after following those in the sense of ‘noting them’…). There’s people only advocating this once prefixes of this group are received from a dynamic feed (like the well-known Team Cymru fullbogons list, disclaimer: this is just an example and I don’t have any commercial relationship with them) which in turn has its own set of intricacies and issues (trust the source of updates? what if this was subverted? contractual controls with the source? trust the transmission mechanism? etc.). See also here for the currently allocated IPv6 address space as of IANA.
  • Anti-spoofing: put your own prefixes here (and make sure you don’t overlook any ;-).

Let’s have a look at the “Current IPv6 martians” list maintained (last on 2015-07-28…) by Job Snijders and to be found here (it’s for route filtering as opposed to ACLs, but for our discussion this doesn’t really matter):

It is mostly a combination of filtering special-purpose addresses (e.g. lines 1–4, 8–15 + 17, 25–27) and filtering unallocated blocks (namely lines 5–7 and 18–24, again also see this IANA link) , and it hence has some elements of several of the categories I introduced above.

Some parts deserve special attention & discussion though. First it should be noted that the first seven lines can be summarized to/replaced by ::/3. Admittedly though this doesn’t look as impressing on the stage of the security theater and/or ‘to the auditors’ 😂…

Furthermore the list contains both the TEREDO (2001::/32) and the 6to4 (2002::/16) prefixes. There is some debate if filtering those is appropriate as one might actually see legitimate traffic (albeit small amounts) from those. For example my friend Jason Fesler, who runs the very useful test-ipv6 site, told me he usually sees about 0.5% traffic coming in from the 6to4 prefix. On the other hand some people argue that 6to4 is so broken anyway that it would be better to filter it completely than expose users to the horrible user experience (then potentially attributed to IPv6) they will go thru via 6to4, e.g. see Gert Doering‘s contribution to the related thread (in May 2019) on “IPv6 ingress filtering” on the ipv6-ops (“IPv6 operators forum”) mailing list (a similar thread on ‘list of IPs to block outbound’ of October 2019 on the NANOG mailing list to be found here). So this would be a case of the above “think about it” category…

I now realize that, when it comes to IPv6 bogon filtering, things aren’t as easy as I presumed when I started writing this post ;-). In a nutshell potential filters in such lists can be broken down to some ‘always filter’ entries, some ‘stay away from this if you don’t exactly know what you’re doing’ pieces and some ‘it depends’ candidates. Whatever you do it will make sense to accurately comment individual entries and why you handle them in the way you do. Your fellow security admins (and the auditors…) will like that. In a follow-up post I might come up with a nicely commented list, for copy+paste purposes… stay tuned. And thank you for your attention while reading!
May 2020 bring lots of IPv6 joy for us.

Updated: Basic IPv6 Troubleshooting Commands / IPv6 Rosetta Stone 2019

Hi everybody,

This post is meant to provide an overview of basic IPv6 troubleshooting approaches and commands, for three main operating systems: Windows, Linux & macOS. For these OSs (and some specific tasks only) it includes an updated version of the “IPv6 Rosetta Stone”, a website I often refer IPv6 beginners to in order to identify OS-specific flavors of relevant commands, but which is a bit outdated as of today.

Continue reading “Updated: Basic IPv6 Troubleshooting Commands / IPv6 Rosetta Stone 2019”

Some Notes on IPv4 Address Space

Most of you will be aware there are currently several initiatives to make IPv4 address space formerly & formally considered ‘special addresses’ – and hence not to be used for common Internet traffic – usable (by some definition of ‘usable’).
The motivation behind such efforts is clear: namely depletion of RFC 1918 space within many organizations, often aggravated by insufficient assignment and distribution schemes in the past. This motivation is understandable. However there is – as will turn out for good reasons – quite some debate about this, and in this post I want to give some technical overview plus provide a bit of perspective, too.

As I laid out in my “A Brief History of the IPv4 Address Space” post the concept of ‘special addresses’ has existed for a long time. The following picture shows the current “IANA IPv4 Special-Purpose Address Registry”:

Looking at this it becomes clear that there are significant differences between them as for their function or scope. There might also be quite some differences as for the actual handling of them on network devices or hosts.

Their ‘can not be routed’ attribute might have a different scope:

  • over the Internet.
  • in transit even within seemingly isolated/closed networks.

This property of not being forwarded across specific links (as explicitly prescribed for some of them in the individual RFCs) can be enforced by different methods:

  • filtering of routing information of such networks (see e.g. RFC 1918).
  • filtering of traffic with a source address from such networks. This is the classic ‘bogon filtering’ performed in many enterprise networks on their Internet uplink devices.
  • filtering of traffic with a destination address of these blocks.

These respective methods can be implemented on different devices:

  • on routers
  • on middleboxes, for example (but not only) firewalls
  • on individual hosts (by means of a local packet filtering component or within the IP stack/on the kernel level).

Furthermore this behavior can be configurable, or not. It might be enabled by default, or not. Operators or sysadmins might be aware of the behavior and/or related config options, or not.
Some of the above intricacies are nicely illustrated in Emile Aben’s RIPE Labs article on “The Curious Case of 128.0/16”.

On the other hand looking at the numbers and the size of some of these blocks it becomes clear that a good chunk of the overall IPv4 address space belongs to the ‘Special-purpose addresses’ which, in times of IPv4 address space depletion ever getting more acute, whets the appetite of people thinking about ways to make them usable. The most prominent initiative is the “IPv4 unicast extensions project”.

The main idea here is to modify the Linux kernel (and others, but the idea was primarily presented in Linux circles) in a way that allows to use various parts of the special address space as regular unicast addresses. The line of reasoning is summarized in a slide set containing this one:

As a long-time Internet enthusiast I have to admit there’s a lot of good thoughts in that presentation. I particularly like the innovation angle and the care for startups.

Still, let’s evaluate the idea from a practitioners’ perspective. As laid out above there’s a variety of handling (usually: suppression) methods and places besides the Linux kernel for these addresses. This in turn makes it probably very hard in a sufficiently large or complex network to create full transparency if/where those addresses are filtered, especially as in the past there wasn’t much need to keep track of their actual handling (as they were dropped anyway, at some point in the network).
Honestly, even without my IPv6 hat (ok, here we are, I mentioned it 😉 ) I would be highly skeptical if the unicast-extensions approach is going to work outside small & isolated environments. E.g. how would one make sure that users from remote corporate sites connecting through different types of SOHO firewalls (different models from different ages) can actually flawlessly connect to data center located services operating on ‘extended IPv4 unicast addresses’?

Finally there’s the question if these addresses are going to be used as another block of private addresses (as the recently added support of in the Linux 5.3 kernel seems to imply) or if those are going to a new pool of ‘available IPv4 addresses’ to be distributed to the public via IANA/the RIRs. In that case, observing IPv4 address space related market dynamics in the last years, those addresses might well & soon end up in the hands of ‘the incumbents’, e.g. large cloud providers. Which wouldn’t exactly help innovators & startups then… but wait, ‘innovators’ are not exactly the population that should learn IPv4 anyway, right? 😉

tl;dr: I do not expect these addresses to be fit for (whatever) purpose within the next 24–48 months in the vast majority of environments.