[colug-432] IPv6

[Rick Troth]

On 11/21/2013 10:11 PM, Richard Hornsby wrote:
> I understand that IPv6 is a 128 bit address, instead of the outdated 32 bit system that we're using today, which has more or less run out of space.  What I'm less clear about is how to use it properly, and how to interpret that really long string into something meaningful.

Yippie! an IPv6 question. This is fun stuff!

> en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> 	ether f8:1e:df:d7:1b:80
> 	inet6 fe80::fa1e:dfff:fed7:1b80%en1 prefixlen 64 scopeid 0x5
> 	inet6 fd5d:4ffd:7d1b:1:fa1e:dfff:fed7:1b80 prefixlen 64 autoconf
> 	inet6 fd5d:4ffd:7d1b:1:8db7:5b1c:f3b0:3bad prefixlen 64 autoconf temporary
> 	inet6 2605:a601:2a1:d101:fa1e:dfff:fed7:1b80 prefixlen 64 autoconf
> 	inet6 2605:a601:2a1:d101:207b:59de:cf87:ce3f prefixlen 64 autoconf temporary
> 	inet 192.168.1.7 netmask 0xffffff00 broadcast 192.168.1.255
> 	media: autoselect
> 	status: active

"temporary" is new to me. All the more strange that it is the one routed
to the public internet.

Are you getting the IPv6 address from your ISP?

> I get "192.168.1.7" and can generally remember that well enough.  I thought that an IPv6 address had something to do with the MAC address, but I'm not seeing it here (some pattern of bytes in common, but not sure it means anything?), and I'm unclear on why there are so many IPv6 addresses configured on this (OSX, admittedly) wireless interface on my home network.  I'm not doing anything special, just standard DHCP(?) provided by the google fiber router box thing that's doing IPv4 NAT as well as IPv6 routing.

The "FE80" address is related to your MAC address. They call it the
"link local" address. It can be used within your LAN but does not get
routed.

The "2605" addresses are typical of public IPv6.

The "FD5D" are new to me. Others on the list know more about IPv6 than I
do. They'll likely chime in.

What's significant is the addresses used for routing. Do an ...

    ip -6 route


... for a quick view of that. (Assuming OS/X has that command.)


> When I look at what my public IP is showing up as, I get
>
> "Your public IP address is 2605:a601:2a1:d101:207b:59de:cf87:ce3f"
>
> which shares the same first 8 bytes (2605:a601:2a1:d101) as one of the inet6 addresses on the interface (but the final 8 seem to come from?)  I also notice that the last ipv6 address on the interface matches the public address.

Right. One of the addresses must be what the outside world sees. It's
unique, not hidden behind NAT. (Well ... that's the short version of the
story, no IPv6 equivalent to 192.168.x.x.)

*This "2605:...:ce3f" is the address you care about.* Question is, how
did you get it?

> I'm really confused, and having a hard time finding information somewhere between IPv6 for dummies "computers use bits, that means 1s and 0s" and the super technical stuff.  Can anyone break it down?  If you understand the IPv6 stuff, do you _really_ type in that really long string in cases where DNS isn't present or available?  

Nah ... don't bother committing the address to memory. Save your brain
for more important work. Put it into DNS or put it into /etc/hosts then
forget it.

I don't think the IPv6 designers ever intended for you to remember an
IPv6 address.

> Speaking of that - I sometimes test connectivity or DNS by using 8.8.8.8 (or, back in the day -- 128.146.1.7 / 128.146.48.7 ;) ) -- easy to remember.  How does anyone remember what the IPv6 equivalent of that (or anything else) is?

A misunderstood aspect of IPv6: _it's a different network._
OS/X and Linux and Windows and most others these days are "dual stack".
The TCP layer is the same. The UDP layer is the same. But the IP layer
... completely independent topology and routing. There is no specific
correlation between IPv4 and IPv6 on the wire.

The _DNS straddles 4 and 6._ You can use 8.8.8.8 and most other public
servers to get either IPv4 "A records" or IPv6 "AAAA records" (aka "quad
A records"). Using my own server as an example ...

    $ host www.casita.net
    www.casita.net has address 173.88.126.238
    www.casita.net has address 198.178.231.250
    www.casita.net has IPv6 address 2001:4978:f:51d::2
    www.casita.net has IPv6 address 2604:8800:12b::1a
    www.casita.net has IPv6 address 2605:4400:1:781:216:3eff:feb2:e7fa


That's three boxes (the content is static so any of them can respond).
All of them are dual stack. For one of them, it's IPv4 address is a
prisoner of IPv4 style NAT.

When you enter the name, your browser hits DNS, gets all of the above,
and picks whichever address (4 or 6) works best.

-- R; <><



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