Subject: [Softwires] SA46T questions (was: Re: FW: SA46T implementation)

From: Nejc Škoberne <[email-masked]>
Date: Mon, 15 Aug 2011 14:43:43 +0100

Dear Naoki,

>> 1. Since we are analyzing IPv4 address sharing mechanisms in general (mostly 4over6 mechanisms), we are interested in the variant of your design, which also includes a NAT somewhere in the network. As far as I understand, the only plance where you can put a NAT device is the core - so with your design, you can only provide "classic" CGN-type of address sharing, is this correct?
> 
> SA46T is just a tunneling technology, that mean, usage of simple
> tunneling technology may possible, and usage with combination with NAT
> may possible.
> 
> As you mentions, SA46T may use CGN-type method, however, I want say
> "address reusable mechanism", not "address sharing mechanism".
> 
> DS-Lite is the technology which combined CGN and tunnel. SA46T may be
> used as tunneling technology in DS-Lite. In such case, SA46T provide
> address reuse mechanisms with SA46T plane ID. Using SA46T plane ID, same
> IPv4 address can be used with different plane ID value.
> 
> I think SA46T may use other than access network. For example, SA46T may
> provide IPv4 VPN service over IPv6 only backbone. I feel softwire WG
> focus access network too much.
> 
> SA46T does not have address sharing mechanism. However, SA46T-AS have
> address sharing mechanism. That is A+P like mechanism.
> 
> SA46T-AS is documented in
> http://tools.ietf.org/html/draft-matsuhira-sa46t-as-01
> 
> In this version, two usages is discussed, one is clients environments,
> and other is server environments.

As far as I can see from the SA46T-AS draft, you just embed 16-bit port
number in the SA46T-AS address, is this correct? This means, you cannot
have a port range, but only 1 port per CPE allocated. I guess I am
missing something here?

Also, you say in the 5th section, that ICMPv4 doesn't work. But for
for this, you can make an ALG, like with other address sharing mechanisms?
I think having ICMPv4 work is quite a crucial thing in such a mechanism.

---

Question to others: what do you think about this? Should I also include
this one into the table of IPv4 address sharing mechanisms?

Thanks,
Nejc

---

From: Naoki Matsuhira <[email-masked]>
Date: Tue, 16 Aug 2011 16:10:05 +0900

Hi. Hejc,

> have a port range, but only 1 port per CPE allocated. I guess I am

That's depend on prefix length. If prefix length is 128bits, only one 
port per SA46T-AS tunnel endpoint is allocated. However, If prefix 
length is 128 - 8 = 120bit, 2^8 = 256 ports per SA46T-AS tunnel endpoint 
are allocated. And also, if prefix length is 128 - 16 =112bit, 2~16 = 
65536 ports per SA46T-AS tunnel endpoint are allocated, and this case 
dose not share one IP address.

Number of ports can be selected by prefix length.

> I think having ICMPv4 work is quite a crucial thing in such a mechanism.

Yes, your comment is correct. I merely describe a general rule. And I 
agree your point.

---

From: Nejc Škoberne <[email-masked]>
Date: Tue, 16 Aug 2011 16:53:01 +0100

Dear Naoki,

> Number of ports can be selected by prefix length.

I see.

So essentially, SA46T-AS is like 4rd, but with a different port-allocation 
scheme. Also the "IPv4 plane" feature (you also call it "IPv4 VPN service")
can be seen as a variant of multiple 4rd domains in 4rd context.

Do you agree? If this is so, I don't really see why would we need a separate
specification for this? I mean, we could also define various port-allocation
schemes in the 4rd draft (as in RFC 6056, where we have various port
randomization algorithms available for implementation).

Thanks,
Nejc

---

From: Naoki Matsuhira <[email-masked]>
Date: Wed, 17 Aug 2011 11:08:11 +0900

Nejc,

Basically, I think your point is correct, and I agree with you.

However, in my honest opinion, I am confused a little about target 
technology in softwire.

SA46T and SA46T-AS is just a tunneling technology.

The other side, in my understanding, DS-Lite and 4rd is combination 
technology of tunneling and NAT.

In my understanding, DS-Lite is CGN + Tunneling combination, so CGN + 
SA46T combination may possible. I think this combination may say DS-Lite.

To similar, 4rd make NAT in CPE assumption. I don't understand 4rd is 
just tunneling function, or combination with CPE NAT. In the standing 
point of SA46T-AS, as you point out, SA46T-AS + CPE NAT combination may 
possible.

Both DS-Lite and 4rd is the combination technology for access network. 
However, I also have interests to apply SA46T-AS to the server environment.

I think your trade-off analysis is very important. If adding 
SA46T/SA46T-AS technology to your analysis table, I think "DS-Lite + 
SA46T" and "SA46T-AS + CPE NAT" is appropriate.

Regards,
Naoki Matsuhira.

---

From: Nejc Škoberne <[email-masked]>
Date: Wed, 17 Aug 2011 10:46:44 +0100

Dear Naoki,

> However, in my honest opinion, I am confused a little about target 

Well, me too. This is why I am trying very hard lately to understand
things first.

> technology of tunneling and NAT.

For DS-Lite, I agree. However, for 4rd NAT is not necessary. As 4rd
draft says:

"Although 4rd is designed primarily to support IPv4 deployment to a 
customer site (such as a residential home network) by an SP, it can
equally be applied to an individual host acting as a CE router."

So if you have a host, acting as a CE router, supporting 4rd technology,
you don't need NAPT44 in it. So in this regard, it is completely the
same as SA46T-AS. At least this is how I understand it.

> SA46T combination may possible. I think this combination may say DS-Lite.

I wouldn't use DS-Lite in any other context, since it is now an
independent Proposed Standard. It is as it is. The tunneling there is
clearly specified.

> point of SA46T-AS, as you point out, SA46T-AS + CPE NAT combination may 

See above.

> However, I also have interests to apply SA46T-AS to the server environment.

Well, not necessarily, why? It's just a technology, I can't see why you
couldn't use it in an enterprise as well?

> SA46T" and "SA46T-AS + CPE NAT" is appropriate.

Well, I don't agree with DS-Lite + SA46T, I would rather make it
"SA46T + CGN". However, since your SA46T-AS already is an address sharing
solution and it mentions NAT in one of the scenarios (in the draft), I don't
think it needs to be combined with anything. So in the end, we have (regarding
SA46T):

- SA46T (tunneling only)
- SA46T+CGN (NAPT44 placed in the core)
- SA46T-AS (directly implemented in the host or NAPT44 placed in the CPE)

Do you agree?

Nejc

---

From: Naoki Matsuhira <[email-masked]>
Date: Thu, 18 Aug 2011 15:39:41 +0900

Nejc,

Your comments are very helpful for me to arrange my confusion. Thank you.

> Well, me too. This is why I am trying very hard lately to understand

I agree.

> same as SA46T-AS. At least this is how I understand it.

I understand.

> independent Proposed Standard. It is as it is. The tunneling there is

I think that I have a point in your opinion.

> couldn't use it in an enterprise as well?

Yes. I also have interests in an enterprise, and P2P environments, too.
As you say, SA46T and SA46T is just a technology. I think SA46T and 
SA46T is just one of the tool for operators and SIers. I hope 
inventiveness should possible in any environments and the future.

> - SA46T-AS (directly implemented in the host or NAPT44 placed in the CPE)

Yes. I agree.

> Nejc

Naoki.