Difference between NAT and NAPT?

[Marko Vojinovic]

In short, what is the difference? Are there any (dis)advantages of
using one over the other?

Best, :-)
Marko

[Nifty Fedora Mitch]

On Sun, Apr 26, 2009 at 05:51:52PM +0200, Marko Vojinovic wrote:
>  
>  In short, what is the difference? Are there any (dis)advantages of
>  using one over the other? 
Put your subject line in a search engine like Google.

  http://www.dcs.gla.ac.uk/~lewis/networkpages/m05s09NAT.htm

For most "mortals" NAT is just fine.
NAPT may be needed on a large private network but 
the hardware/ software has to work harder and thus
may cost more.




-- 
	T o m  M i t c h e l l 
	Found me a new hat, now what?

[Marko Vojinovic]

On Tuesday 28 April 2009 07:51, Nifty Fedora Mitch wrote:
>  On Sun, Apr 26, 2009 at 05:51:52PM +0200, Marko Vojinovic wrote:
>  > In short, what is the difference? Are there any (dis)advantages of
>  > using one over the other?
>
>  Put your subject line in a search engine like Google.
>
>    http://www.dcs.gla.ac.uk/~lewis/networkpages/m05s09NAT.htm
>
>  For most "mortals" NAT is just fine.
>  NAPT may be needed on a large private network but
>  the hardware/ software has to work harder and thus
>  may cost more. 
Well, I was already beginning to worry if my post made it to the list at 
all. :-)

Of course, I did do some research on the subject, but all that I found was 
described in a very general way, and consequently vague. So I was hoping to 
start a conversation with someone knowledgeable, in order to get more 
concrete answers.

My setup consists of three to five computers and a small wireless router, with 
an adsl uplink utilizing a dynamic public IP address (just a single one, the 
m=1 case in the article you quoted). What I would like to understand better 
is the following:

* Why does my ISP's router manual insists on using NAPT over NAT? The ISP tech 
support admitted to not understand why and have no explanation, but 
nevertheless they suggested that I set up the router as the manual says. Is 
there a general well-known reason for insisting on such a setup?

* Is there a performance penalty in using NAPT over NAT? Packets have to be 
altered and reassembled in both cases, so should I really expect any notable 
time difference here?

* Given my setup from above, is there a serious need to use NAPT over NAT? If 
yes, why? If not, why not? (note: I consider muself just a simple mortal with 
a small home network, nothing too fancy)

* I understood that NAT is about mangling the source IP address of the packet 
so one could push more local IP addresses through less public ones. I fail to 
understand the further gain of mangling tcp/udp port numbers? Can you provide 
an example situation where NAPT works and NAT doesn't, so I can visualize the 
difference in packet travel?

* Is it probable that the NAT setups I have created in the past (typically on 
Linux machines playing as routers, using mostly firestarter built-in NAT 
support) were actually NAPT setups, while I wasn't explicitly aware of the 
difference? IOW, is it maybe usual to say/write NAT in software manuals while 
actually meaning NAPT instead?

I tried to do my homework here, but these questions somehow just weren't quite 
answered in any NAT vs NAPT articles I could find on the net. I would 
appreciate any hints in understanding all this a bit better.

Thanks, :-)
Marko

[Nifty Fedora Mitch]

On Wed, Apr 29, 2009 at 11:49:13PM +0200, Marko Vojinovic wrote:
>  On Tuesday 28 April 2009 07:51, Nifty Fedora Mitch wrote:
>  > On Sun, Apr 26, 2009 at 05:51:52PM +0200, Marko Vojinovic wrote:
>  > > In short, what is the difference? Are there any (dis)advantages of
>  > > using one over the other?
>  >
>  > Put your subject line in a search engine like Google.
>  >
>  >   http://www.dcs.gla.ac.uk/~lewis/networkpages/m05s09NAT.htm
>  >
>  > For most "mortals" NAT is just fine.
>  > NAPT may be needed on a large private network but
>  > the hardware/ software has to work harder and thus
>  > may cost more.
>  
>  Well, I was already beginning to worry if my post made it to the list at 
>  all. :-)
>  
>  Of course, I did do some research on the subject, but all that I found was 
>  described in a very general way, and consequently vague. So I was hoping to 
>  start a conversation with someone knowledgeable, in order to get more 
>  concrete answers.
>  
>  My setup consists of three to five computers and a small wireless router, with 
>  an adsl uplink utilizing a dynamic public IP address (just a single one, the 
>  m=1 case in the article you quoted). What I would like to understand better 
>  is the following:
>  
>  * Why does my ISP's router manual insists on using NAPT over NAT? The ISP tech 
>  support admitted to not understand why and have no explanation, but 
>  nevertheless they suggested that I set up the router as the manual says. Is 
>  there a general well-known reason for insisting on such a setup? 
With ADSL and a handfull of systems there will be little difference.

Stick with the ISP's documentation and recommendations.
Both of you will be on the same page should you need to fix anything.

The wikipedia notes are good enough.  See the section "Drawbacks, Benefits".
   http://en.wikipedia.org/wiki/Network_address_translation
And see also:
   http://en.wikipedia.org/wiki/Port_address_translation
Do lookup and read the RFCs...

Since you are on ADSL I suspect you are very limited in the list of services you
can expose on their network.  In the normal case you only have one changeable IP address 
so famous services when permitted will have to be 'targeted' to a fixed host
inside
and without some external Dynamic DNS service will be undiscoverable by the world.



-- 
	T o m  M i t c h e l l 
	Found me a new hat, now what?