How to generate IPv6 RA without any prefixes?

[Bjoern A. Zeeb]

On Thu, 18 Nov 2010, sthaug at nethelp.no wrote:

Hi Steinar,

>>> In IPv6 it should be possible to generate a Router Advertisement which
>>> contains no prefix options (the idea being that I want the host to
>>> populate its default router list but nothing else). However, I cannot
>>> seem to get rtadvd to do this.
>>>
>>> If I start rtadvd with no /etc/rtadvd.conf file, it sends RAs with a
>>> prefix option corresponding to the IPv6 address of the interface. In
>>> the /etc/rtadvd.conf I can explicitly specify prefixes ("addr"), but
>>> I can't find any way to specify that no prefix options should be sent.
>>>
>>> Any suggestions?
>>
>> What if you start rtadvd with -s and have a basically empty (default)
>> config file entry?
>>
>> I haven't checked but theat would be my best guess?
>
> Does not appear to work. With /etc/radvd.conf containing only:
>
> vlan0:\
>        :raflags#128:
>
> and starting rtadvd with -s, it still announces the /64 prefix I have
> on the vlan0 interface.
>
> It's possible we simply have some missing functionality here. The man
> page for Mac OS X shows an "addrs" field which FreeBSD doesn't have -
> but which still doesn't do quite what I want:
>
> http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man5/rtadvd.conf.5.html
>
> addrs   (num) Number of prefixes.  Its default is 0, so it must explicitly
>         be set to positive values if you want to specify any prefix
>         information option.  If its value is 0, rtadvd(8) looks up the
>         system routing table and advertise the prefixes corresponding to
>         interface routes on the interface.  If its value is more than 1,
>         you must specify the index of the prefix for each item below.
>         Indices vary from 0 to N-1, where N is the value of addrs.  Each
>         index shall follow the name of each item, e.g., ``prefixlen2''.

we'll have to redo some of rtsol(d)/rtadvd anyway as IANA has (long)
assigned valid magic numbers for the formerly experimental options
from the initial days.

Can you open a PR and get it assigned to net@ or bz@, so this won't be
lost?  I am not sure I'll be able to look the next 10 days.

/bz

-- 
Bjoern A. Zeeb                              Welcome a new stage of life.
         <ks> Going to jail sucks -- <bz> All my daemons like it!
   http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/jails.html