why use IPv6, was: Lazy network operators

Iljitsch van Beijnum iljitsch at muada.com
Sun Apr 18 08:32:16 UTC 2004


On 18-apr-04, at 4:48, Paul Jakma wrote:

>> Oh oh I see another one taking the path that leads to the dark side.

Michel, you forgot to include the audio: 
http://www.bgpexpert.com/darkside.mp3

> Well, let's be honest, name one good reason why you'd want IPv6
> (given you have 4)?

Let me count the ways... At home it's great because of the extra 
address space. I have a /29 at home, which is pretty luxurious compared 
to what most people have, but not nearly enough to give all my boxes a 
real address if I turn them all on at the same time. Worse, I still 
haven't figured out a way to give some machines always the same address 
(if available) but also use that address for something else if the 
"owner" is turned off. In IPv6 all of this is a breeze: a single /64 
gives you all the addresses you'll ever need and boxes configure 
themselves with the same address each time they boot, even when using 
different routers and no need for DHCP.

Another thing I really like about IPv6 is the much smarter "on-link" 
behavior. In IPv4, it's not uncommon to have two hosts on the same 
physicial subnet, but with addresses from different prefixes. These 
hosts will then have to communicate through a router, which in this 
time of cheap 10/100/1000 cards usually isn't the fastest option. In 
IPv6 each subnet prefix has enough addresses to hold all hosts that you 
can possibly connect to a layer 2 network in the first place. But it 
also handles this situation much better, if it comes up: routers can 
advertise additional prefixes as "on-link" so hosts know they can reach 
destinations in those prefixes directly over layer 2. Redirects also 
work across prefixes. (Similarly, routing protocols use link local 
addresses which make it possible to run RIP or OSPF between two routers 
that don't share any prefixes.)

Since there is no need for NAT, every IPv6 host can run a server for 
any protocol without trouble.

Because of the large address space, scanning address blocks is no 
longer an option.

If you have multiple routers, you pretty much have HSRP/VRRP 
functionality automatically.

Renumbering is much easier.

It's also very handy to be able to log in to a box, completely screw up 
its IPv4 configuration and rebuild it from scratch without having to 
worry that the host becomes unreachable and needs a powercycle.

> And, to be more on-topic, name one good reason
> why a network operator would want it? Especially given that, apart
> from the traditional bleeding edges (academic networks), no customers
> are asking for it.

I think "no customers" is rounding it down slightly. Yes, demand is 
low, but so is supply, hard to tell which causes which. And customers 
who do ask, are routinely turned down.

> As Paul Vixie points out, without a multihoming solution beyond that
> offered by 4, v6 networks will look just v4 - most of it will be on
> non-global address space and NAT. Not really interesting..

Multihoming can be done the same way many people do it for IPv4: take 
addresses from one ISP and announce them to both. Obviously your /48 
will be filtered, but as long as you make sure it isn't filtered 
between your two ISPs, you're still reachable when the link to either 
fails. However, this means renumbering when switching to another 
primary ISP. Not much fun, despite the fact that renumbering is much 
easier in IPv6.

> [snip darth vader]

> I know, what's worse is that I know it need not be so. (how's your
> MHAP doing?  How's Iljitsch's geo-assigned addressing proposal?)

Michel is no longer in the IPv6 business, and I've failed miserably at 
convincing people that geographic aggregation is helpful here. So 
currently, multi6 is looking at approaches that allow transport 
protocols to jump addresses in the middle of a session.




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