| ## 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
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
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
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
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.
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