unum at unum5.org
Wed May 27 15:29:59 MDT 2009
Jones, Scott (GE Money, consultant) wrote:
> At the risk of sounding ignorant, what is the difference functionally
> between the uplink being plugged into the WAN port versus into one of
> the LAN ports?
The main thing is the Network Address Translation(NAT). If you can turn
that and DHCP off I don't know that there would be any difference. In
order to communicate on the Internet each device needs to have an IP
address. In order to reduce the number of IP addresses required(and
possibly for a small security benefit) many consumer grade routers pull
a trick where they allow all the computers plugged into them to use one
ip address. This is what I'm referring to when I talk about NAT. So
the NAT device sees two worlds. The WAN and the LAN, and it has two ip
addresses. When it talks to the internet it uses its WAN IP when it
talks to your network it uses it's LAN IP. If a computer on the LAN
requests data from the internet, that request goes to the NAT device
where it is repackaged to look like it is coming from the NAT
device(with the WAN IP), but is specially marked so the NAT device can
remember which computer made the request. Then when the request in
answered it is sent back to the NAT device that then repackages it and
sends it back to the computer that asked for it. If a computer on the
LAN side asks for data from another computer on the LAN side then the
device just sends the data between the two like a regular switch with
out any repackaging.
The other difference is DHCP. Basically if you plug a cable into the
WAN port the device will ask for an IP Address if you plug a cable into
the LAN port the device is going to expect to give out an IP Address.
So if you plug one NAT device's LAN port into an other NAT's device LAN
port without disabling DHCP they will both be answering DHCP calls and
trying to give out IP Addresses and routing information. Which can
cause all sorts of problems.
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