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## Aliasing with PPP
## Dan Langille <>

This article deals with setting up PPP aliases. This will allow other computers to use your FreeBSD box as a gateway to your ISP. I will assume that you already have PPP installed and running. If you haven't installed PPP yet, you may wish to read the of The FreeBSD Diary or Issue #4's PPP article.

What is a gateway?

A gateway is a link to another place. Your computer can be a gateway to your ISP for other computers. It's pretty darn easy to make FreeBSD act as a gateway. Just add the following line to your /etc/rc.conf file:

	gateway_enable="YES"	# Set to YES if this host will be a gateway.

The easiest way to implement this change is to reboot. You can avoid the reboot by issuing the following command instead of rebooting:

	sysctl -w net.inet.ip.forwarding=1

But in either case, make sure you make the change to /etc/rc.conf so that the next time you reboot, the machine acts as a gateway.

What is an alias?

An alias is another name for something. In networking terms, it's a method for translating one set of IP addresses for another set. Aliasing is also known as Network Address Translation (NAT) and IP Masquerading. Most commonly, aliasing is used to convert private addresses on the inside of a gateway to public addresses on the outside of a gateway.

For more a bit information on aliasing, see the of The FreeBSD Diary, but come back here because you don't really want natd if you have PPP. Or so I've been told.

Adding aliasing to your PPP setup

The reference for this section is and I suggest you read that first.

I added the following line to the default section of /etc/ppp/ppp.conf:

	alias enable yes

The has an excellent section on to use your newly created gateway.

Testing the aliasing

All of these tests assume you are using another box on your network and not your gateway box unless otherwise specified. I am also assuming you are using dial-on-demand.

The easiest way to this this setup is to use one of your other computers and trying pinging your ISP. Your modem should dial and the pings should start. If it does, you've got it right! If you can't try pinging from your gateway box. If your modem dials up, then your other machine doesn't have the gateway properly specified. See .

The next step is to browse to your ISP's homepage. If you can't do that, then try the same thing on your gateway box. If it works on your gateway box, then the other box does not have the DNS server set correctly. It should be set to your ISP's DNS server. If you are running a DNS on your gateway box, set it to that.

If you can't browse to a website, try browsing to an IP address. Use nslookup to get the IP address and enter that address into the browser. If that works, then it's definitely a DNS issue. The machine does not have it's DNS server specified properly. Again, see for more information.

- Dan

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