Re: [Softwires] sharing restricted addresses by hosts in 4rd (draft-despres-intarea-4rd-01)

[Mark Townsley <[e-mail]>]

On Apr 19, 2011, at 4:06 PM, Alain Durand wrote:

> 
> On Apr 12, 2011, at 4:03 PM, Mark Townsley wrote:
> 
>> 
>> Hello Dmitry,
>> 
>> My view is that 4rd is most easily understood if and only if it connects to a CE function that is performing NAPT. The CE function may be in what is traditionally considered a host, or in what is clearly a router.
>> 
>> More specifically, a device that is forwarding packets from one interface (virtual or otherwise) to another through a NAPT that has one interface with IPv6 configured (via DHCPv6 or otherwise) as performing 4rd (which enables dual-stack via a port-restricted IPv4 address for the NAPT using IPv6 as the transport) then you a have a 4rd CE. That could be a "host" in that it is a Windows PC with internet connection sharing for IPv4 turned on and hence forwards packets between interfaces with a NAPT due to the IPv4-enabled interface created when 4rd is configured. 
>> 
>> I would avoid anything that requires the host forwarding table to be altered to accommodate 4rd. Instead, the NAPT function that is already present in a small router or host configured to look like a router is modified to use a set of ports that it is allowed to use when 4rd is enabled. 
> 
> 
> Mark:
> 
> How would an app running on a 4rd CPE communicate in IPv4 to another app running on another 4rd CPE?

First, by definition any 4rd CPE has IPv6. So, if your application works with IPv6. 4rd-to-4rd is as easy as knowing two IPv6 addresses and not having a simple-minded firewall between the two blocking traffic.

For IPv4, in the model I describe above, all applications are sitting behind the NAPT within the CPE bound to the 4rd tunnel. End-to-end looks just about as desperate and ugly as it does today between any series of NAPTs and firewalls. Skype will make its way through, I suspect with no modifications. 

- Mark

> 
>   - Alain.
>