IPv6 security: Everything old is new again

One of the first problems facing any layer three protocol is address resolution.

One of the first problems facing any layer three protocol is address resolution. Given an IP packet, how to deliver that to an Ethernet interface?

IPv6 uses a protocol called the Neighbor Discovery Protocol (NDP) to do address resolution, among other things. Neighbor Discovery (ND) uses multicast to a small set of similar addresses rather than a broadcast to all, but in broad terms is very similar to IPv4's ARP. The router builds a cache of layer three to layer two mappings. For new destination IPv6 addresses the router sets up a new cache entry, sends out an ND solicitation, and waits for the desired host to respond with its layer two address. If the router receives no response within a certain time, it discards the cache entry; otherwise it completes the cache entry and can then use it to deliver packets to that destination IPv6 address.

If someone sends lots of packets for non-existent IPv6 addresses, the router will end up with lots of incomplete cache entries. If enough such packets are received fast enough, all available cache slots may be used up, meaning that no new addresses can be reached. Since completed cache entries time out after a little while, even good entries may be dropped, to be replaced by new never-to-be-completed entries. Unlike most other NDP-related attacks, this one can come from outside your network. It doesn't take much bandwidth either – timing out an incomplete cache entry takes about four seconds; in four seconds a gigabit link can deliver more than enough packets to be a problem.

Sadly there is no real defence yet. Bad packets are indistinguishable from good packets; the router can't tell that an address doesn't exist unless it does neighbor discovery on it. The simple defence of having a big enough cache to handle the load is not feasible with IPv6, where just a single subnet has billions of possible addresses. You can mitigate the problem by doing things like using small subnets, filtering packets at your border, rate limiting and so forth, but the real defence lies in sophisticated cache management in the routers.

Another NDP issue is rogue router advertisements. Setting up an IPv6 “router” is trivial on any modern desktop or laptop. An on-link host sending unwanted router advertisements can cause havoc – deprecating prefixes, redirecting traffic and so on.

There are two solutions in the wings, but neither is complete or robust yet. The first is Secure Neighbor Discovery, or SEND. SEND uses cryptographically generated addresses and signed NDP messages, guaranteeing that the apparent sender of an NDP message is in fact the sender. Combined with a mechanism for distributing certificates (a PKI), SEND is a solution to rogue RAs; without a PKI, it is not. SEND is a moderately heavyweight solution, but a bigger issue is that neither Windows nor OSX currently support SEND.

A second solution is RA-Guard. RA-Guard is (conceptually) a piece of software that sits at a security border such as a switch, and inspects passing RA messages. If they meet certain criteria, RA-Guard lets them pass. If they do not, RA-Guard blocks them. This sounds simple enough, but it turns out that IPv6 throws a few curve balls – current implementations get confused by extension headers, for example. Fixing this means either redefining the NDP protocol to forbid extension headers, or building lots of wire-speed layer three smarts into switches.

Karl Auer is technical manager at IPv6Now, a company specialising in helping organisations get into and get the most out of IPv6. This is the third in a four-part series of articles on IPv6 security issues.

Follow @CSO_Australia and sign up to the CSO Australia newsletter.

Join the CSO newsletter!

Error: Please check your email address.

Tags Networkingsecurityipv6

More about etwork

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by Karl Auer

Latest Videos

  • 150x50

    CSO Webinar: Will your data protection strategy be enough when disaster strikes?

    Speakers: - Paul O’Connor, Engagement leader - Performance Audit Group, Victorian Auditor-General’s Office (VAGO) - Nigel Phair, Managing Director, Centre for Internet Safety - Joshua Stenhouse, Technical Evangelist, Zerto - Anthony Caruana, CSO MC & Moderator

    Play Video

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

More videos

Blog Posts

Market Place