v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space

Owen DeLong owen at delong.com
Mon Feb 9 23:47:11 UTC 2009

On Feb 9, 2009, at 3:33 PM, Mark Newton wrote:

> On 10/02/2009, at 9:54 AM, Stephen Sprunk wrote:
>> Yes, an ALG needs to understand the packet format to open pinholes  
>> -- but with NAT, it also needs to mangle the packets.  A non-NAT  
>> firewall just examines the packets and then passes them on unmangled.
> Sure, but at the end of the day a non-NAT firewall is just a special  
> case
> of NAT firewall where the "inside" and "outside" addresses happen to
> be the same.

Uh, that's a pretty twisted view.  I would say that NAT is a special
additional capability of the firewall which mangles the address(es)
in the packet.  I would not regard passing the address unmangled
as a "special case" of mangling.

In terms of implementing the code, sure, the result is about the same,
but, the key point here is that there really isn't a benefit to having  
packet mangling code in IPv6.


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