NAT ? Or not to NAT? What's the difference?

[mjpearson]

Ok, I think I understand the concept of NAT but in the new Linksys E-xxxx routers, you can disable NAT. What does that do? Does the router now act just like a switch and passes the data through the Internet side to the LAN side without address translation?

I must be missing something here.


mike

 

[SYQUEST]

In the user guide on page 8 & 9 read the following:
----------------------------------------------------
Advanced Routing
NAT
Enabled/Disabled If this Router is hosting your network’s
connection to the Internet, keep the default, Enabled. If
another router exists on your network, select Disabled.
When the NAT setting is disabled, dynamic routing will be
available.

Dynamic Routing (RIP)
Dynamic routing uses the Routing Information Protocol
(RIP). This option enables the Router to automatically
adjust to physical changes in the network’s layout and
exchange routing tables with other router(s). The Router
determines the network packets’ route based on the
fewest number of hops between the source and the
destination.
Enabled/Disabled When the NAT setting is enabled, the
Dynamic Routing option is automatically disabled. When
the NAT setting is disabled, this option is available. Select
Enabled to use the Dynamic Routing option.
-----------------------------------------------------------
Maybe you should read the user guide! It is pretty self explanatory, unless you don't understand IP routing. Then you should educate yourself, and find some good tutorials covering the subjects.

....JIM....

 

[mjpearson]

Thanks Jim,

Actually, I read the manual several times before posting and it still doesn't make sense to me. The tutorials that I've read pretty much read the same. Big on jargon but weak on explanation.

Here's my confusion. I'm trying to figure out how to configure the IP address of the Internet port and the respective LAN port(s). Do they in fact become the same IP address since they aren't NAT-ed and they reflect the same device within the same network segment. Or do they need to be independent IP address and then you use the ROUTE settings to link them together? I have yet to find a tutorial that explains it.

 

[SYQUEST]

I see your dilemma. Unless you have a background in Ethernet networks, and/or routing with devices like Juniper Networks, Fortinet, Sonicwall, or Cisco, those concepts probably elude you. The Linksys option to disable NAT, changes the way the router functions. If the router is NOT connecting to the Internet, but instead another network, then you would DISABLE NAT, and you build your own routing table of static routes, or use RIP and the router will dynamically add some for you, but only destinations it discovers or it acquires from listening to broadcasts on the network. It is a way to join two or more networks together. The basics of a router is like a yard with gates. The software and configuration provide the guide lines on how the router will work, or in other words: determine who goes in, out, or not through the "gates", or the conditions needed to go through the "gates". Most of the SOHO routers like Linksys, Netgear, Belkin, etc. have basic routing functions "fixed" so you are limited in what you can configure. With routers like Juniper, Fortinet, Sonicwall, or Cisco, you build the entire configuration from scratch! Almost nothing is there for a default route.

Hopefully, this sheds some light on the subject. So when using the Gateway or Internet option of the Linksys routers, all outgoing traffic takes on the single IP address assigned to the WAN interface (many to one). Which is the only "NAT" you will get from these devices. Most don't provide ANY 1-2-1 NATting anymore. All you get is port forwarding, which is NOT NAT on the reverse side!

....JIM....

 

[kurio71]

Mike, are you connecting the Wan port of a second router into the Lan port of a router that is connected to the internet? Thus trying to create another segment in your network. If you are you need to disable NAT on the second router and configure a static route. The first segment (the DMZ) won't know about the second. Some SOHO routers won't do this well though.

 

[mjpearson]

Thanks Kurio,

That makes more sense. As I thought about it more and more about the subject, it was puzzling me why offer such an option in the router for the home user? It seems so odd. But as you've suggested, it is a way to do some segmenting and isolation. Now I just have to find an application that needs such service so I can hook it up and play with it.

mike

 

[SYQUEST]

You would be surprised how many businesses use the cheap SOHO Linksys stuff. So that is why it is there, and as more network/LAN stuff is used in the home environment more features and functions are needed for different things...

....JIM....