Router Help (NAT)

[Siar]

So i've been having, seemingly, isolated internet problems of late and in trying to figure it out i've been learning more about how routers work and the recommended settings.

In doing so i came across NAT- i'm not sure what this does but it has an option to either set for a single IP or multiple IP's.

Its currently set to single but i dont know if I should change it to multiple or not. Currently at home we have setup with the router plugged into a Hub and everyone else's computers plugged into the hub.

Any tech wiz out there that can advise?

 

[wheunis]

NAT, or Network Address Translation, is a function that allows a router to mask all the internet traffic generated by the LAN nodes, as if it was generated from itself.

What does this mean?
This means that when you access a site or service with NAT enabled, the site will read your address as the WAN address of your router.

What is it needed for?
Mostly, for web browsing, you don't NEED to use NAT, but it surely does help with security. Not using NAT exposes your LAN's addresses when they use the internet; A potential entry point for hackers onto your LAN, as your internal IP's are now visible to them.
Some services, like online gaming, require NAT. Even if you choose to not use NAT, you can still use such services, but this means you will have to lease your own static internet IP's for each machine that needs to use that service.


What does all this mean for you?
NAT is a good feature and should be on at all times, for all machines. It would be best for you to refer to the router's manual; From what I am simply guessing, it would be best to enable NAT for multiple (ie: all machines).
NAT should only ever be disabled in certain conditions, which for the average user = never.

 

[Pada]

Nice explanation wheunis, but you've made a big mistake by saying the following:

Some services, like online gaming, require NAT.

No services require NAT. NAT is actually a big problem when you're trying to host something behind a router with NAT enabled on its WAN connection. When NAT is enabled and you want to host something from a PC on the LAN, you'll have to port forward.
If you want to avoid port forwarding, then you can simply dial a PPPoE connection from the PC, since it would bypass the NAT.

All ADSL routers have NAT enabled by default, unless you change the router to bridge mode only. If the router is dialing the PPPoE connection and does not have NAT enabled, then no PCs on the LAN would have Internet connectivity since the ISP won't know where to route the LAN IP addresses too. Of course the packets from the LAN would reach the ISP with NAT disabled, but the ISP can't return any packets.

NAT is must have when you want to provide Internet access for nodes with private IP addresses (used on LANs, like 10.0.0.0/8, 172.16.0.0/12 & 192.168.0.0/16). In this case, its not necessary to NAT on the first router though, but you'll have to NAT on the router that has the public IP address with Internet access.

 

[wheunis]

Pada:

You actually can browse and such with NAT disabled. The router will simply revert to the smaller brother of NAT, ie: PAT (Port Address Translation). This is the same as using ICS in Windows.

However, gaming and such on PAT = a nightmare, because you cannot forward anything at all. PAT also has ZERO internal firewall capability.

But, it should be noted, that "cheaper" routers do not include PAT capabilities at all, and thus disabling NAT will disrupt connectivity completely, yes.

 

[Pada]

wheunis:
If you disable NAT then you shouldn't be able to browse either, unless the router is implementing a transparent HTTP proxy server.

Nowadays everyone refers to 'NAT', but actually we should've referred to it as 'NAT overloading' or 'PAT'.
If the routers simply implemented 'NAT' (without overloading), then only 1 PC would've been able to have Internet access via the router, unless you had multiple public IP addresses. Strictly speaking, NAT is a 1 to 1 IP address mapping (usually private IP address mapped to a public IP address).
Here's where I got that from: http://cisco.com/en/US/tech/tk648/tk361/technologies_q_and_a_item09186a00800e523b.shtml

 

[Siar]

weird, we have three computers running off the router with the default single IP option toggled and it seems to work. What i'm getting from this is that it would be better if i toggled the multiple IP's option?

 

[wheunis]

Dunno Siar.

The option as you described it can mean many things. It would help if you refer to your router's manual to check the actual setting's description.