Mini-How-To Turn My Laptop Into A Wifi Access Point

From Sfvlug

Yeah, right! I'm sitting in my hotel room with my wife and my brother-in-law and there's a note sitting on the table, Wifi Internet access is available, for only $12.95 per day per computer. Or, $11.95 per day in three day blocks. Do the math here folks, that's $358.50 per month. Do you pay that much at home? Of course not, so how do they justify such an exorbitant fee? I just happen to be a person who doesn't like getting ripped off, and that, to me, is a rip off. I also happen to be a person with an EVDO card. Plus I happen to be a Linux user, so here goes.

First of all, I just connect my laptop to the Internet with my EVDO card. That's fine, but my brother-in-law wants to get online as well, and he's got Vista (your pity is already understood). Next, I connect one of those Airlink AR-430W routers I brought with me to my ThinkPad.

So here's the situation with the AR-430W, it will act as a DHCP server to the wireless network it creates, as well as being a DHCP client to its uplink provider. My solution is to actually double NAT. I created a simple network between the router and my laptop, and also turned my laptop into a router.

Next, configure the ThinkPad as a router, DHCP server, and DNS server. It only takes three steps to make this happen, enable the sysctl for routing, masquerade the outbound packets, and fire up dnsmasq. I know the AR-430W router is issuing DHCP addresses on the network, so I picked as the middle network.

service NetworkManager stop
ifconfig eth0 up
dnsmasq -a -F,
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A PREROUTING -o ppp0 -j MASQUERADE

Now, packets from the AR-430W NAT from their 192.168.1.x address to, and on their way to the Internet, NAT from to whatever IP my EVDO card has. This is really simple stuff, actually. I just needed a place to write this down so next time I'm travelling and need this, I can easily access it.


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