An update of IPv6 in FreeBSD

Bjoern Zeeb did a lot of work in FreeBSD to have ip6 running smoothly. He started his talk with a quick poll: how much of the audience would be allowed to reach ip6-only sites? He was surprised to see about 30% of the audience raising their arms. He then askes who had native ip6 connectivity at home. About half lowered their arms.

Table of Contents

1 FreeBSD and the World IPv6 Day

The World IPv6 Day took place on the 8th of June, 2011. The goal was to have several "content providers" enable ip6 on their sites, for at least one day. Google (on the main domain), Facebook (on a sub-domain), Yahoo!, Akamai were participants. The FreeBSD main website had been accessible over ip6 for quite a long time before the World IPv6 Day. For FreeBSD, the following took place:

  • created ip6-only snapshots, in which support for AF_INET is compiled out;
  • communication: web pages, a dedicated and rather active IRC channel.

It was mostly a non event. Bjoern showed a graph of ip6 connections to the website: nothing interesting is visible on the World IPv6 Day. We do notice a slight traffic increase over a long time range (several month). There are significant peaks of ip6 traffic during the week-ends.

1.1 What happened during the day

Requests for filtering ip6 fragments. Some packets have a Fragment header, since only the end-points are allowed to do ip6 fragmentation, not the routers. Some devices (which ones?) send packets with such headers, but with only one fragment in the sequence. This is at least dubious. Whether this is allowed is unclear, this is kind of a grey area in the RFC.

Report of one possible ip6 panic in 7.4. Unfortunately, not enough information was given to trace back, and the reporter is no longer reachable (only popped up on IRC?).

Issues with ip4 mapped addresses (??? to investigate).

A lot of downloads of the ip6-only snapshots. A lot of them from ip4 connections! Hypothesis: this was for internal networks which work over ip6, or maybe just for fun…

2 ip6-only validation work

Today, ip6-only connectivity is mostly useless on the public internet. About 4% of users can reach ip6-only services.

2.1 What the point, then?

First reason: this is interesting and fun! Removing ip4 support from the kernel actually started as a April's fool joke.

Second, more serious reason: when ip6 does take off, FreeBSD doesn't want to be left behind, it needs to be ready feature-wise.

Personally, Bjoern is interested in ip6 for the usual reasons. He pointed out a reason I had never heard so far: NAT breaks geo-localisation and makes following users on their IP address more difficult. As a result, targeted ads will slowly become less relevant when large-scale NAT start being deployed. So, ad-selling parasites content producers will want to push ip6.

2.2 How to do ip6-only in the kernel

In your kernel configuration:

nooptions INET

nodevice gre (this is a bug, GRE tunnels should work).

In src.conf, define WITHOUT_INET_SUPPORT.

Tweak the features in sysctl(8) in the net.inet6 tree.

2.3 How to do ip6-only in user-space

Need to add support in ifconfig(8) and in the rc framework. With a command such as ifconfig interface addr, ifconfig would assume the inet family for the address. This is obviously not going to fly when ip6 addresses need to be configured… The general direction will be to make the inet6? keyword mandatory.

Jails were interesting. Both ip4-only and ip6-only jails have been supported for some time, but an ip6-only kernel caused some issues (I don't remember more details).

Don't rely on a usable 127.1 address :-)

Different degrees of ip6-readiness were observed:

  • some software does not work with ip6 at all;
  • some software works in dual-stack hosts, but start breaking if ip4 is not configured;
  • some software works in dual-stack hosts where ip4 is not configured, but start breaking when ip4 is not available at all in the kernel;
  • some software works in a ip6-only kernel.

Most utilities will just work without ip4. bsdinstall and pc-sysinstall know how to handle ip6-only kernels (bsdinstall is the new installer for 9.0).

ftp(1) was an example of the 3rd situation: the ftp client needs to know the size of a socket. It tries to open a dummy AF_INET socket, which fails in an ip6-only kernel…

All software that uses gethostbyname(3) will break. Some software uses getaddrinfo(3). However, while bsnmpclient(3) uses getaddrinfo(3), it passes the ai_family = AFINET option :-/. There is mush work left to get rid of old DNS interfaces.

There are sometimes confusing error messages. fetch(1) for instance: in a broken ip6 network, when called without options to get a file from a DS host, it would report Address family not supported by protocol family. When called with the -6 option (to force ip6), it would report No route to host 1.

What would happen was that in the first case, fetch(1) would try an ip6 connection, fail because of some network issue, then try an ip4 connection, fail because AF_INET is not available, give up and print the last error according to errno. In the second case, fetch would try ip6, fail, give up because the -6 switch told it to not try ip4 and print errno. In this instance, fetch was actually doing things right, but reported only the last error, which was not the important one.

3 What has improved

What has been largely tested:

  • NFS
  • HAST
  • bsdinstall
  • NTP, but some issues with ip6 multicast

More fixes to base are expected after 9.0.

4 How to help

Test, test and test!

Remove your ip4 addresses; try in ip6 jails; try a real no-inet kernel.

Test everything in the base system. Report both success and issues.

5 ip6 in 9.0 and beyond

Random improvements all around are expected:

  • SeND
  • ipfw
  • rtadvd / rtsold:
  • resolvconf(8) script ?
  • support for working as a CPE: in this configuration, FreeBSD is both a host (on the ISP side) and a router (on the home side).
  • follow CERR, an informational RFC for CE routers
  • more ifconfig options:
    • no RA
    • not default interface
    • NUD
    • no RADR (don't add routers learnt from RA)
    • no linklocal
  • tempaddress (don't use, don't prefer) 2
  • R-bit in NA
  • the rc.conf framework:
    • handling of more details
    • mandatory inet6 keyword in the configuration
    • ipv6+privacy (Bjoern cited a concern: without privacy extensions, *BSD hackers always have the same host portion, but a changing network portion as they go from one conference to another; a dedicated netadmin could use that to follow their movements between different networks…)
  • control the default AF

Java has some issues with v4-mapped addresses.


1 Citing from memory; the second might have been Network unreachable, but that's the general idea.

2 I must have misunderstood what Bjoern meant, because at least basic support is available since 5.2. Maybe he meant something more granular then the current global setting?

Auteur : Frédéric Perrin (fred CHEZ resel POINT fr)

Date : 2012-12-16 18:43:07 CET

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