>>I have NetBSD 1.6.1RC3 installed and I noticed following behaviour in
>> autoconfiguration. The autoconfigured addresses dissapears every once
>> and a while for a few seconds. What I noticed was that this happens
>> every time the address has been configured for a valid life time
>>although the host has received a number of router advertisements during
>> this time.
>
> 	the basic suggestion is, as documented in rtadvd(8), do not have
> 	rtadvd.conf and let rtadvd(8) determine what prefix to be advertised
> from interface configuration in the kernel.  use rtadvd.conf only when
> you are sure really about it.

But if I'll remove the prefix from the rtadvd.conf then the rtadvd will
advertise the prefix with it default valid life time and with default
preferred life time which are 2592000 and 604800 seconds although I still
have a valid life time of 60 seconds and preferred life time of 30 seconds
in the rtadvd.conf. That's why I have defined the prefix in the
rtadvd.conf in order to be able to change the valid and preferred life
time of the prefix.

>>E.g. if I have configured at my IPv6 router in rtadv.conf following:
>> xl0: \
>>   :addrs#1:addr="2ffe:300:20:3e00::":vltime#60:pltime:30: \
>>   :maxinterval#4:mininterval#3:rltime#60:
>
> 	there's a typo: pltime#30, not pltime:30.  maybe it is the cause?

That was not the problem that was my copy paste mistake.

Here is an example of Router advertisement captured with ethereal when no
prefix has been defined in the rtadvd.conf:
0000  33 33 00 00 00 01 00 60  08 bd f4 fa 86 dd 60 00   33.....` ......`.
0010  00 00 00 38 3a ff fe 80  00 00 00 00 00 00 02 60   ...8:... .......`
0020  08 ff fe bd f4 fa ff 02  00 00 00 00 00 00 00 00   ........ ........
0030  00 00 00 00 00 01 86 00  c1 07 40 00 00 3c 00 00   ........ ..@..<..
0040  00 00 00 00 00 00 01 01  00 60 08 bd f4 fa 03 04   ........ .`......
0050  40 c0 00 27 8d 00 00 09  3a 80 00 00 00 00 2f fe   @..'.... :...../.
0060  03 00 00 20 3e 00 00 00  00 00 00 00 00 00         ... >... ......

As you can see the valid life time is 0x00278d00 and the preferred life
time is 0x00093a80 which are the default values for rtadvd.

  Jan