IPv6 Confusion

Tony Hain alh-ietf at tndh.net
Tue Feb 17 19:28:11 UTC 2009

While people frequently claim that auto-config is optional, there are
implementations (including OS-X) that don't support anything else at this
point. The basic message is that you should not assume that the host
implementations will conform to what the network operator would prefer, and
you need to test.

One last comment (because I hear "just more bits" a lot in the *nog
community)... Approach IPv6 as a new and different protocol. If you approach
it as "IPv4 with more bits", you will trip over the differences and be
pissed off. If you approach it as a "different protocol with a name that
starts with IP" and runs alongside IPv4 (like we used to do with decnet,
sna, appletalk...), you will be comforted in all the similarities. You will
also hear lots of noise about 'lack of compatibility', which is just another
instance of refusing to recognize that this is really a different protocol.
At the end of the day, it is a packet based protocol that moves payloads


> -----Original Message-----
> From: Carl Rosevear [mailto:Carl.Rosevear at demandmedia.com]
> Sent: Tuesday, February 17, 2009 10:58 AM
> To: Owen DeLong
> Cc: nanog at nanog.org
> Subject: RE: IPv6 Confusion
> Thanks to all that responded on and off-list.  My confusion is mostly
> cleared-up.  The points that are unclear at this point are generally
> unclear to most people, it seems due to lack of operational experience
> with IPv6.  Feel free to keep responding to this topic as its all very
> interesting but I think my needs have been met.  Owen, this one from
> you tied it all together.  Thanks all!
> --Carl
> -----Original Message-----
> From: Owen DeLong [mailto:owen at delong.com]
> Sent: Tuesday, February 17, 2009 10:41 AM
> To: Carl Rosevear
> Cc: nanog at nanog.org
> Subject: Re: IPv6 Confusion
> On Feb 17, 2009, at 8:59 AM, Carl Rosevear wrote:
> > So, I understand the main concepts behind IPv6.  Most of my peers
> > understand.  We all have a detailed understanding of most things
> > IPv4.  I have Googled and read RFCs about IPv6 for HOURS.  That
> > said, to quickly try to minimize people thinking I am an idiot who
> > asks before he reads, I need some answers.  First of all, several of
> > my friends who feel they are rather authoritative on the subject of
> > things network-related have given me conflicting answers.  So what's
> > the question? ...
> >
> > How does IPv6 addressing work?
> >
> There are a lot of different possible answers to that question, many
> of which are accurate.
> In general:
> It's a 128 bit address.  Routing is done on VLSM, but, generally for
> DNS purposes, these
> are expected to be at least on nibble boundaries.
> There is an intent to support what is known as EUI-64, which means
> every subnet should
> be a /64, however, there are people who number smaller subnets and
> that is supposed
> to work, but, it will break certain IPv6 things like stateless
> autoconfiguration (which is
> optional).
> > I know it's been hashed and rehashed but several orgs I am
> > associated with are about to ask for their allocations from ARIN and
> > we are all realizing we don't really know how the network / subnet
> > structure trickles down from the edge to the host.  We really don't
> > have a firm grasp of all of this as there seems to be multiple
> > options regarding how many addresses should be assigned to a host,
> > if the MAC address should be included in the address or if that is
> > just for auto-configuration purposes or what the heck the deal is.
> > There are a lot of clear statements out there and a lot that are
> > clear as mud.  Unfortunately, even when trying to analyze which RFC
> > superseded another.  Can I just subnet it all like IPv4 but with
> > room to grow or is each host really going to need its own /84 or
> > something?  I can't see why hosts would need any more addresses than
> > today but maybe I'm missing something because a lot of addressing
> > models sure allow for a huge number of unique addresses per host.
> >
> You can subnet it just like IPv4.  Each host does not need it's own
> subnet (/64, not /84 for the most part).
> The theory behind /64 subnets was to support a way for a host to use
> what it already knows (MAC
> address) and possibly some additional clues (Router Announcement) from
> the wire to configure
> its own IPv6 address on an interface.  Whether or not this was a good
> idea is still controversial, but,
> whether or not it's how IPv6 is going to work is not.  IPv6 is
> designed to work with Stateless
> Autoconfiguration whether we like it or not.  DHCPv6 so far is
> prevented from providing
> default router information (or many of the other things you're used to
> having DHCP do)
> as it currently stands.
> >
> > My buddy and I are about to go to Barnes and Noble, not having and
> > luck with standard internet media but then we realized...  how will
> > we know if any of that is really what we are looking for either?
> >
> It's a fair point.  There is a good FAQ/Wiki on the ARIN web site.
> That may be a good place to
> start.
> >> From what I can tell, this may still be a question of great
> >> debate.  Everyone seems to act like they know exactly what's going
> >> on but behind closed doors admits that they don't really know x, y,
> >> or z.  I realize this is typical of my industry and even myself
> >> from time to time.  J
> >
> > But so I am truly reaching out here.  What is the deal with IPv6
> > addressing and subneting? Where is the official guide to this new
> > galaxy?  I will be sure to pass this information on to my equally
> > less clueful peers to the benefit of all of us that are making this
> > transition.
> >
> Officially, the best summary I can give is that the subnetting model
> is almost identical to
> IPv4, but, all subnets should be at least a /64 (and it's hard to
> imagine a scenario where
> a single subnet should be larger, but, it can be supported).
> The essential initial guidelines are:
>         ISP             /32
>                         Enough for 4billion ISPs
>                         Enough for each ISP to support 65,536 /48
> customers or 16.7M /56
> customers, etc.
>                         Larger ISPs can get more than a /32 if needed.
>         End Site        /48
>                         Enough for 65,536 /64 subnets
>                         Larger organizations can get more than a /48 if
> needed.
>         Single Subnet
>                         /64
>                         Enough for more hosts that most of us can
> imagine on a single subnet.
>                         Support for 64 bit MAC addresses
>                         Support for stateless autoconfiguration
> However, these guidelines can be violated in many circumstances to use
> smaller
> subnets if you really want to.  I don't recommend it and there's
> really no reason to
> do so.
> Finally, if we're wrong about all of this, it's OK.  We can renumber
> people into
> the other 7/8ths of the IPv6 space that are not yet issued for usage
> by IANA
> with an entirely different numbering scheme.
> > There are people here at my company that seem to get it but can't
> > seem to explain it clearly to me.  To me, its basically just larger
> > addressing space with some new logical boundaries....  But there are
> > so many discussions of potential addressing methods that I am
> > confused.   I know from my lab setups that I can "make it work" but
> > I'd like to "do it right".  J
> >
> Hope the above helps.
> > I've been doing this for over 10 years now...   IPv4 is native to
> > me.   If you can point me in the direction of some good,
> > authoritative information or even say "Dood, go get IPv6 for
> > dummies", that's fine I just need to know where to find some good
> > information.
> >
> Unfortunately, other than the guidelines above, most of us are still
> experimenting
> and don't have a lot of op-ex to build on.
> > Can someone say "well, you know how it would be nice to have like
> > 100 different addresses on hosts to differentiate services and blah
> > blah....  Well now that's what you account for and so then you know
> > how a /24 almost always ends up being tight in IPv4?  Right, so
> > think of your basic bit boundaries that you adhere to as /??
> > And /???   In IPv6."   Or "Throw all that old thought out the
> > window.    Now its kind of like how the Ford Probe is actually a
> > Mazda...  ummm....  Yeah I can't really explain it either but it
> > makes sense.  Here read this book and it'll make sense to you too."
> >
> Your basic bit boundary for a subnet really should be /64.  You
> certainly can put
> as many IP addresses on a single host as you wish and there's no
> reason not
> to address services as you describe.  There is no longer a concern
> about the
> tightness of the subnet since a /64 is the square of the total number
> of hosts
> that could be supported on the entire internet without
> network/broadcast
> overhead, etc.
> In IPv6, there really is no shortage of addresses and extremely little
> likelihood
> of that ever being a problem, even with the wasteful allocation
> polices we
> currently have in place.
> Hope that helps,
> Owen
> (Speaking only as and for myself.  This is not an official position or
> recommendation
> from the ARIN AC.  I'm just trying to help.)

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