Diffrences: IPv4 vs IPv6

Robert E. Seastrom rs at seastrom.com
Wed Jan 25 14:50:54 CST 2012

Alex Fraser <beatnic at comcast.net> writes:

> I would like to start playing with IPv6.   I'm retired, my
> experimental net would be paid for out of my "toy money", so cost is
> important.  I'm connected to the internet through Comcast. I'm
> assuming  (but don't really know) that I can have a home network
> connected to the internet using IPv6.  I'm fairly comfortable with a
> couple of flavors of Linux, but have a couple of workhorse XP
> machines.  I use a Linksys wireless router connected to the cable
> modem, which uses NAT to give my home computers addresses which they
> pick up with DHCP.

So far so good.  You're in a great position to run IPv6 at home.

> So assuming I can get the Comcast cable modem to use IPv6, could I
> get a new image to burn into my Linksys router to let it route IPv6
> to my home network.  I have a couple of the Linksys boxes running
> dd-wrt now.  It would be sweet to have IPv4 and IPv6 running on my
> home net at the same time so I could phase in the upgrade.  So where
> do I start? Must I register for some IPv6 addresses to use at home
> or is there an equivalent of the non routable NAT address blocks
> like in IPv4?

OK, so let's start with a few points:

You don't register IPv6 space from a central registry yourself for
your home, just like you don't for IPv4.  You get it from an "upstream
ISP", but in the case of Comcast, though they're running trials it's
not something you can get "on demand" from them.  So you have to
tunnel it in over IPv4 using a protocol called "6in4".  This is a very
close cousin of the "IP in IP" encapsulation that KA9Q NOS has run for
20 years or so - it's just building a tunnel to an upstream ISP which
you can get IPv6 connectivity from.  These folks are called "tunnel
brokers".  Hurricane Electric is a popular one that has a tunnel
endpoint box in Ashburn.


The good news is that (assuming you're running a relatively new, and
not stripped-down-due-to-having-shitty hardware copy) DD-WRT supports
IPv6 out of the box, and there are howto documents that should get you started.


Hurricane will give you a /48, or /64 prefix (I think) for your end
site depending on what you ask for.  Remember that a /64 is a single
LAN (LANs are always /64 - there are advantages and disadvantages to
this as others on the list can tell you), but the upshot is that you
never have to worry about how much space for host addresses you have
on the network since just as there are 64 bits in the prefix, there
are 64 bits in the host section, meaning a theoretical 2^64 hosts on
the network.  How big is 2^64?  If you drained all five Great Lakes
and filled them with almond M&Ms, you would have about 2^64 M&Ms...
and 2^65 calories...  which corellates with a weight gain of about
3*10^61 pounds.  I gotta get back on my diet.

You don't NAT IPv6 traffic - you can put in a firewall/filter in your
dd-wrt router to express policy about who can talk to your machines,
but NAT is a big pain in the butt and requires working around.

With the instructions I've linked you to, you should be able to get
IPv6 up and running in an evening.

If you're running Linux of a Mac, stateless autoconfiguration should
do the job and you'll get an IPv6 address:

Billet:~ rs$ ifconfig en1
     ether 00:26:bb:0e:f3:33 
     inet6 fe80::226:bbff:fe0e:f333%en1 prefixlen 64 scopeid 0x5 
     inet netmask 0xfffffe00 broadcast
     inet6 2610:178:1:2:226:bbff:fe0e:f333 prefixlen 64 autoconf 
     media: autoselect
     status: active
Billet:~ rs$ 

Note that I have two IPv6 addresses on my wireless interface here: a
link-local address (the one that starts with fe80::) and a globally
unique one (the one that starts with 2610:178).  The Mac picked up its
address via stateless autoconfig.  MacOSX 10.7 "Lion" does DHCPv6 too.

The utilities for testing IPv6 are ping6 and traceroute6, thus:

Billet:~ rs$ ping6 ipv6.google.com
PING6(56=40+8+8 bytes) 2610:178:1:2:226:bbff:fe0e:f333 --> 2001:4860:800e::68
16 bytes from 2001:4860:800e::68, icmp_seq=0 hlim=55 time=34.783 ms
16 bytes from 2001:4860:800e::68, icmp_seq=1 hlim=55 time=27.008 ms
16 bytes from 2001:4860:800e::68, icmp_seq=2 hlim=55 time=26.834 ms
--- ipv6.l.google.com ping6 statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 26.834/29.542/34.783/3.707 ms

Billet:~ rs$ 


Let me know how things work out for you, and if you need any more help
or if I've glossed over stuff that has left you with an information


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