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Installing PPP - alias 24 March 1999
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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 Installing PPP.
Note: alias is being deprecated
The -alias option on ppp is being replaced with the -nat option.  Eventually, it will be removed altogether.
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 natd 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 titled IP Aliasing and can be found at http://www.freebsd.org/tutorials/ppp/.   I suggest you read that first.

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

alias enable yes

The PPP - Pedantic PPP Primer has an excellent section on Configuring Windows Systems 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.

The easiest way to this this setup is to use one of your other computers and trying pinging your ISP.  Your modem should dial.  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 Configuring Windows Systems.

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.  See Configuring Windows Systems.

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.  See Configuring Windows Systems.

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