v6 subnet size for DSL & leased line customers

Robert E. Seastrom rs at seastrom.com
Fri Dec 28 02:50:01 UTC 2007

Leo Bicknell <bicknell at ufp.org> writes:

> In a message written on Thu, Dec 27, 2007 at 10:57:59PM +0100, Iljitsch van Beijnum wrote:
>> It is wih IPv6: you just connect the ethernet cable and the RAs take  
>> care of the rest. _You_ _really_ _don't_ _need_ _DHCP_ _for_ _IPv6_.  
>> If you need extreme control then manual configuration will give you  
>> that, which may be appropriate in some cases, such as servers.
> Really.  I didn't know RA's could:
> - Configure NTP servers for me.
> - Tell me where to netboot from.
> - Enter dynamic DNS entries in the DNS tree for me.
> - Tell me my domain name.
> - Tell me the VLAN to use for IP Telephony.
> Those are things I use on a regular basis I'd really rather not
> manually configure.

I'm running (native) IPv6 at home, and in the colo too.  Most of my
ssh sessions to personally owned machines go over v6.

My laptops (with a single exception) are Macs.  You may not be aware
that the Mac is fairly smart about which interface it uses for
connections - it will prefer the gigabit ethernet to the wireless when
it sees link...  it prefers wireless to dialup too.  Basically,
whenever you establish a new outgoing session it will use the "lowest
cost" interface to do the deed.

For IPv4, I have the same address manually assigned on the DHCP server
to both the gigabit ethernet's MAC address and the wireless
interface's MAC address.  This means that when I plug into the gige,
as I do for filesharing or backing some files up, the Mac uses the
gigabit ethernet.  When I unplug and carry the Mac to the conference
room, *all existing upper layer sessions are preserved* - TCP and
friends are blissfully unaware that a change has taken place; one
gratuitous arp so the router knows where to send the packets and we're
on our way again with nary a hiccup.  I don't have an ssh session
croak just because I connected or disconnected a cable.

I'd really, really, really like to have DHCP6 on the Mac.  Autoconfig
is not sufficient for this task unless there is some kind of trick you
can do to make the eui-64 come out the same for both interfaces (don't
think so).

Anyone from Apple reading this list?  :-)


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