IPv6 Network Administration

Gotchas

Once a computer has IPv6 enabled it is likely to begin to find records relevant to IPv6 in the DNS. In an ideal world, this would cause no problems, even if the device was not connected to the IPv6 Internet. However, a bug in some DNS servers has caused then to respond with a "host does not exist" message, rather than a "no record of this type" message. The best known occurrence of this led to IPv6 users not being able to connect to news.bbc.co.uk unless they first looked up its IPv4 address, although this problem has since been resolved. Others have had problems with ad.doubleclick.net, where some of its servers do not respond to queries for IPv6 addresses.

Native IPv6 over Ethernet uses multicast at the link-level for a number of things, and thus is sensitive to the correct operation of multicast in Ethernet drivers. There have been several reports of vendors discovering that Ethernet multicast is broken only when users complain that IPv6 does not work correctly.

The usual manifestation of this is that Neighbor Discovery behaves oddly. One way to test this is to run a tool such as tcpdump that puts the Ethernet interface into promiscuous mode. This means that the Ethernet interface examines all packets, thus working around incorrect filtering of multicast packets. If IPv6 seems to work correctly while the interface is in promiscuous mode, there's probably a multicast problem. You will need to contact your vendor for a fix.

One other confusing thing that can happen is that ...