What makes a good IPv6 implementation?

datePosted on 12:23, November 23rd, 2018 by Craig Miller

Bad IPv6 support costs Money

I have been working with Docker lately, and as cool as the container technology is, it was originally built without consideration for IPv6, and then IPv6 was bolted on later. Making supporting IPv6 full of expensive work-a-rounds.

But that got me thinking what makes a good IPv6 implementation? Of course this is my opinion, and you are free to toss in other criteria, so think of this as a thought starter.

Why is this important?

With 25% of the internet carried over IPv6 as of this writing, if you are developing a product which has a lifetime of 5 to 10 years, and you aren’t giving thought as to how you will support IPv6, then your product will:

  • A) fail, or
  • B) you will try to bolt on IPv6 on the side, or
  • C) have to be completely rewritten.

All of that costs money.

A good IPv6 device implementation

There are broad areas where IPv6 should work well.

Addressing

As much as I like the simplicity of SLAAC (Stateless Address Auto Config), there are certainly use cases where DHCPv6 is a better choice. A good implementation should:

  • Support both addressing methods, SLAAC, and DHCPv6
  • Be able to reestablish IPv6 GUA (Global Unique Address) once the device comes out of sleep/suspend or link down/up (systemd suffers this problem)
  • Play well with DNS. Very few of us enjoy typing IPv6 addresses, the implementation should have a stable IPv6 address which can be entered into DNS without requiring a lot of DNS churn.

Routing

IPv6 is not IPv4 with colons. There are somethings which are different for good reason.

  • Default routes are link-local addresses (Docker fails on this one big time). GUAs may change, link-locals shouldn’t.
  • Supports RA (Router Advertisement) fields, RDNSS (DNS server), and DNSSL (DNS domain search list). Not much use having an address if the host can’t resolve names
  • If the device is routing (such as Docker) then support DHCPv6-PD, and provide the option of prefix delegation into the container/downstream network.

Resiliency

Basic protection from network misconfiguration, or out right attacks makes the IPv6 device better prepared for production use.

  • Rational limit on the number of IPv6 addresses an interface may have. Before systemd, the Linux kernel defaulted to 16. This seemed like a good compromise. Back in systemd v232, it was possible to exhaust memory on an IPv6 host by feeding it Random RA addresses, creating a denial of service. FreeBSD v11.5 has a similar problem, where the system will add over 3000 IPv6 addresses, and the system will slow to a crawl.
  • Rational limit on the number of neighbours. IPv6 /64 networks are sparsely populated and therefore one shouldn’t have to expect to support all 16 Quintilian (2^64) neighbours. Something like 1000, or even 256 should be enough.
  • Don’t assume that the Linux Stack has your back. Since systemd has become widespread, there are many IPv6 systemd bugs, which weren’t there in the pre-systemd kernel days. IPv6 is a different stack, be sure to test it.

Summary

I am sure I missing a few, but this is a start. When developing a product, the business case for supporting IPv6 well, is that it will save you money in the long run, by not having to go back and try to bolt IPv6 on, or rewrite your network stack later.

P.S I wouldn’t recommend putting Docker into production because of the severe IPv6 limitations. I’ll be looking at LXC next.

Image: Yachts colliding: Creative Commons/Mark Pilbeam

 

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