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Author Topic: 6to4 subnetting and routing  (Read 3157 times)

nholland

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6to4 subnetting and routing
« on: March 08, 2011, 02:27:03 AM »

Hi folks,

well, I have the following problem. I've already solevd it with regard to IPv4 (which is easy, as I know my way around there), but wouldn't know how to deal with it concerning IPv6. So, let me explain first what I've done IPv4-wise (all Linux boxes):

Code: [Select]
DSL router (PPP:dynamic public IPv4 address + Eth0:192.168.178.1)
|
Box1 (Eth0:192.168.178.40 + Eth1:192.168.0.1)
|
Box2...n (Eth0:192.168.0.2...n)

You see, I've got two subnets at home and I've set them up the way one would normally do. That is, 192.168.0.2 has its default route point to 192.168.0.1, and the DSL router received a static route to 192.168.0.0 via 192.168.178.40, which itself has IPv4 forwarding turned on. Works fine.

Now I'd generally like to do the same with IPv6. And that's where trouble begins. Actually, my DSL router is set to establish a 6to4 tunnel, that is, it gets assigned a /48 based on its current public IPv4 address (which is dynamic and changes regularly). It also automatically seems to assign a /64 to every host "it can see", which would be Box1 in the above example.

Now, what about Box2...n, those boxes "behind" Box1, on another physical network segment? How would I get IPv6 addresses to these in the above scenario?

Solutions I could probably imagine:

1) Subnet the /64 given by the DSL router to Box1 and assign smaller subnets to Box2...n. I guess it's not really encouraged to further subnet /64's though. And I would probably have to add static routes via Box1 to my DSL router. In a situation where my IPv6 prefix is subject to regular change. Would that work anyway?

2) Probably I could also just manually take a /64 and give it to the second (Box2-facing) interface of Box1. That would probably also require routes to be set up in the DSL router, again in a situation where my prefix changes regularly.

Of course I know what would certainly work: Setting up a tunnel (for example, from HE.net) directly on Box1 and use that instead of whatever my DSL router does with its 6to4 stuff. However, at some point in the future my DSL router would probably get assigned "real native" IPv6 prefixes from my ISP (technically, it supports that), and in that case, I would not really want to use an additional tunnel to get my second subnet to work with IPv6 (although, assuming an ISP would give its customer a static prefix, things might be simpler then).

Anyway, does anyone have a clue what to do in a situation like the one pictured above?
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cholzhauer

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Re: 6to4 subnetting and routing
« Reply #1 on: March 08, 2011, 05:16:38 AM »

You need two /64's for your setup, which means you use the /48 you described.

Since that /48 is dynamic, you're going to be stuck manually updating the routes or writing some sort of script that does it for you.

I personally think it would be easier to get a tunnel from HE and use that.  If/when your ISP does go to native IPv6, just stop using your tunnel.

Like you mentioned, you don't really want to go smaller than a /64, which is what RA needs to work.
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nholland

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Re: 6to4 subnetting and routing
« Reply #2 on: March 08, 2011, 05:59:08 AM »

The "use another tunnel for now" approach would certainly work fine, and the more I see the added complexities that other routes would cause, the more I favor it. But...:

Does anyone have an idea how native IPv6 will most likely be handled by big, consumer ISPs in the future? If my ISP assigned me a static /48 for as long as I'm their customer (which I hope would be the case!), things would be fine, as I'd have a static prefix and could set up my routing just as I originally intended. However, if ISPs assign "dynamic" /48s to their customers, just like the assign dynamic IPv4 addresses today, then I'd still be as stuck as I am today, as dealing with a changing prefix sucks.

I sure hope that every customer would get his own /48 that never changes, but as no major ISP here in Germany does currently provide native IPv6, I have absolutely no proof that this would actually be the case.
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Ninho

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Re: 6to4 subnetting and routing
« Reply #3 on: March 11, 2011, 09:46:57 AM »

Does anyone have an idea how native IPv6 will most likely be handled by big, consumer ISPs in the future? If my ISP assigned me a static /48 for as long as I'm their customer (which I hope would be the case!), things would be fine, as I'd have a static prefix and could set up my routing just as I originally intended. However, if ISPs assign "dynamic" /48s to their customers, just like the assign dynamic IPv4 addresses today, then I'd still be as stuck as I am today, as dealing with a changing prefix sucks.

If I had to guess, I'd bet they ISPs will do their best effort not to do the right thing thus making your/our lives miserable - unless you/we are willing to pay for "enhanced" services. BICBW, one can only hope competition will benefit us consumers. Not optimistic though.

Cheers

--
Ninho
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