Subject: Re: Comment on draft-palet-v6ops-proto41-nat-03.txt

From: [email-masked]
Date: Fri, 14 Nov 2003 16:13:39 +0100

Hi Jordi, 

>Yes, you're right. My feeling is that it could be implementation 
dependent, but not sure right now.

Ok! Then, let's continue the analysis I have started at beginning of this 
thread. Suppose the order in which a router will process a packet with 
PF=41 is implementation dependent (as you suggest, although I think this 
is more theoritical option than practical, but nevertheless it might exist 
and it's good to analyse it for sake of completness of our analysis). 

So, let's  suppose now that the first action the router will take when it 
gets an incoming 41-packet is to act as a 6to4 router, instead of applying 
proto-41 immidiately. Then, the router  decapsulates the packet and looks 
what the IPv6 dest address is. If the prefix of the IPv6 dest address 
equals the 6to4 /48  router prefix, the packet is forwarded to its final 
destination (standard 6to4 way of processing the packets), otherwise, the 
I-D says it is forwarded to fixed node in the private network. 
Now, my question is "Which is this node?" Observe, at this level the 
router already works with IPv6 packets and it cannot apply proto-41 which 
is exclusively defined for IPv4 packets. If such forwarding (as you 
describe in the document) takes plays, then it is not proto-41, it is 
simply IPv6 forwarding. 

Sumarizing, the analysis in the whole thread shows that either you  apply 
6to4 or proto-41 transition mechanism but not mixing them. And this is my 
argument when I say if they coexist in a NAT box they should be 
implemented as two independent modes. 
I think this should be written very clearly in the draft in order to avoid 
misunderstanding. 

Greetings, 
Mariana
-----------------------------------------------------------------------------------------------------------------
Dr. Mariana Nikolova 
Philips Research Laboratories Eindhoven (IST/SwA/DS)
Prof. Holstlaan 4, 5656 AA, Eindhoven, The Netherlands
room: WDC 1.35,     phone: +31-40-27-45455
e-mail: [email-masked] 
-----------------------------------------------------------------------------------------------------------------

"JORDI PALET MARTINEZ" <[email-masked]>
Sent by: 
[email-masked]
13-11-2003 18:47
Please respond to "JORDI PALET MARTINEZ"

        To:     <[email-masked]>
        cc:     (bcc: Mariana Nikolova/EHV/RESEARCH/PHILIPS)
        Subject:        Re: Comment on  draft-palet-v6ops-proto41-nat-03.txt
        Classification: 

Hi Mariana,
 
Yes, you're right. My feeling is that it could be implementation 
dependent, but not sure right now.
 
Definitively we need to work more on this.
 
Regards,
Jordi
----- Original Message ----- 
From: [email-masked] 
To: JORDI PALET MARTINEZ 
Cc: [email-masked] 
Sent: Thursday, November 13, 2003 11:00 AM
Subject: Comment on draft-palet-v6ops-proto41-nat-03.txt

Hi Jordi, 

I have a comment on the following paragraph in Section 5 of your draft 

"6to4 and Proto-41 forwarding can coexist in the same NAT box. In that 
case, an IPv6 over IPv4 packet received, will be forwarded to the private 
LAN only if the IPv6 destination does not belong to the local  6to4 /48 
prefix. Otherwise it will be decapsulated in the NAT box, following 6to4 
procedures. This fact avoids the problems created by mobile users when 
they visit a network that uses 6to4, in the case they have some automatic 
proto-41 setup. "

Let's analyze how a router works when it's simultaneously supports 6to4 
and proto-41 mechanisms  as you proposed above. 

If there is an proto-41 entity such as (source IPv4 address, target IPv4 
address, ID=41) in the NAT table of the router, then the so called prerouting is done for all packets matching this entity. Note, this is the first 
action taken by the router  before any other actions are taken. With other 
words, the router forwards all incoming IPv4 packets with PF=41 to the 
target IPv4 address before even decapsulating them and looking what the 
IPv6 dest address is.  So, what is written above "an IPv6 over IPv4 packet received, will be forwarded to the private LAN 
only if the IPv6 destination does not belong to the local  6to4 /48 
prefix. Otherwise it will be decapsulated in the NAT box, following 6to4 
procedures."  does not work in practice, because it require that the router first 
decapculates and  looks the IPv6 dest. ad! dress. 

Summing up, I do see that 6to4 and proto-41 can coexist n the same NAT box 
but rather as two separate modes, i.e. the router can switch between 6to4 
and proto-41 depending of certain preferences as the default one is 6to4 
for example.  In fact, I see the applicability of proto-41 in IPv4-only 
NAT boxes, but if the latter are upgraded to 6to4 routers it seems to me 
overdone to keep proto-41 as well.   

Greetings, 
Mariana
-----------------------------------------------------------------------------------------------------------------
Dr. Mariana Nikolova 
Philips Research Laboratories Eindhoven (IST/SwA/DS)
Prof. Holstlaan 4, 5656 AA, Eindhoven, The Netherlands
room: WDC 1.35,     phone: +31-40-27-45455
e-mail: [email-masked] 
-----------------------------------------------------------------------------------------------------------------

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