Comment on draft-palet-v6ops-proto41-nat-03.txt

[mariana.nikolova@philips.com]

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: mariana.nikolova@philips.com 
-----------------------------------------------------------------------------------------------------------------