ipv6 host part

[JINMEI Tatuya /神明達哉]

>>>>> On Fri, 29 Apr 2005 18:32:48 +1000 (EST), 
>>>>> Neo-Vortex <root at Neo-Vortex.net> said:

>> >> - assuming the prefix is "P/64", do the followings:
>> >> # ifconfig IFNAME inet6 P::1 prefixlen 64 alias autoconf
>> >> # ifconfig IFNAME inet6 P::2 prefixlen 64 alias autoconf
>> >> # ifconfig IFNAME inet6 P::3 prefixlen 64 alias autoconf
>> 
>> > IIRC, the first address within the prefix should have a prefixlen of 64,
>> > (providing the prefixlen is actually 64) but others on the same prefix
>> > should have 128.
>> 
>> I don't remember any such restriction.  What is your source (e.g.,
>> RFC) of this information?

>      alias   Establish an additional network address for this interface.  This
>              is sometimes useful when changing network numbers, and one wishes
>              to accept packets addressed to the old interface.  If the address
>              is on the same subnet as the first network address for this
>              interface, a non-conflicting netmask must be given.  Usually
>              0xffffffff is most appropriate.

> That is for IPv4 taken from ifconfig(8), one would assume for IPv6 it is
> the same and i use it like that without issues (although i have not tried
> it the other way)

The semantics is totally different in IPv6, at least protocol-wise.
IPv6 allows an interface to have multiple addresses with the same
prefix (and length).  RFC3041 (temporary addresses for privacy) is an
example.

You could also assign addresses whose upper 64bits are the same with
the prefix length of 128 if you want, but it's not a requirement.

(Perhaps the man page needs a revise, but it's a separate issue.)

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					jinmei at isl.rdc.toshiba.co.jp