<h1>Setup</h1>
<p>This setup was done on an <a href="https://www.intel.ca/content/www/ca/en/products/boards-kits/nuc.html">Intel Nuc</a>.</p>
<p>The Nuc is running Ubuntu Server 18.04 Bionic, CLI only. It has a wired
connection to a rack switch on an access port, and a wireless connection to the
office WiFi.</p>
<p>The server will host 192.168.0.1 and act as a gateway for the wired servers.
It will do NAT just like a home router does to ensure there are no routing
problems with the upstream layer 3 devices.</p>
<p>This setup begins where my <a href="ubuntu-bionic-wifi">Ubuntu WiFi Guide</a> left off.
Check it out if you're not sure how to connect to the WiFi from an Ubuntu
server.</p>
<h1>Enable IP Routing</h1>
<p>Check if it's enabled in your config file. This command will just print the
file and ignore any comments or blank lines.</p>
<pre><code>cat /etc/sysctl.conf | grep -v -e "#" -v -e "^$"
</code></pre>
<p>If you don't have this entry, edit the file and insert it:</p>
<pre><code>net.ipv4.ip_forward=1
</code></pre>
<p>If you changed the file, apply your changes:</p>
<pre><code>sysctl -p
</code></pre>
<h1>Configure Interfaces</h1>
<p>Here's my netplan, with the wireless details changed:</p>
<pre><code>network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      dhcp4: false
      addresses:
        - 192.168.0.1/24
  wifis:
    wlp2s0:
      dhcp4: true
      access-points:
        "My SSID":
          password: "My Password"
</code></pre>
<p>If you changed your netplan file, apply the changes with</p>
<pre><code>netplan try
</code></pre>
<h1>Configure NAT</h1>
<p>We'll use <code>iptables</code> for NAT.</p>
<p>First, make a file that defines the rules you want:</p>
<h2>Define iptables rules file</h2>
<p>These rules will take any traffic coming from 192.168.0.0/24 that are being
routed out the WiFi interface <code>wlp2s0</code> (the default gateway / default route),
and apply the MASQUERADE rule which will run port address translation, allowing
internet.</p>
<p>There are two tables, <code>nat</code> and <code>filter</code>. The NAT table does the translation,
the filter table defines what's allowed in and out. We need to specify that
traffic is allowed to go:</p>
<ul>
<li>From the Ethernet port to the WiFi port</li>
<li>Back from WiFi to Ethernet, when it is <code>RELATED</code> or <code>ESTABLISHED</code></li>
</ul>
<p><code>vi /etc/iptables_rules.sh</code></p>
<pre><code>#!/usr/bin/env bash
echo "Loading rules..."
iptables -t filter -A FORWARD -i enp0s25 -o wlp2s0 -j ACCEPT
iptables -t filter -A FORWARD -i wlp2s0 -o enp0s25 -m state \
  --state RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o wlp2s0 -j MASQUERADE
echo "Done"
</code></pre>
<p>Make the script executable</p>
<pre><code class="language-bash">chmod +x /etc/iptables_rules.sh
</code></pre>
<h2>Load iptables rules now</h2>
<p>Run the new file to apply the rules.</p>
<pre><code class="language-bash">/etc/iptables_rules.sh
</code></pre>
<p>You can now use this device as a router without having to configure any special
routes.</p>
<h2>Configure iptables rules to load on boot</h2>
<p>Add the following line to your rc.local file. If it doesn't exist, create it.</p>
<p><code>vi /etc/rc.local</code></p>
<pre><code>/etc/iptables_rules.sh
</code></pre>
<p>If the file didn't exist, make sure that it starts with a shebang:</p>
<pre><code>#!/usr/bin/env bash
</code></pre>
<p>Ensure that it's executable:</p>
<pre><code>chmod +x /etc/rc.local
</code></pre>


<h1>Setup</h1>
<p>This setup was done on an <a href="https://www.intel.ca/content/www/ca/en/products/boards-kits/nuc.html">Intel Nuc</a>.</p>
<p>The Nuc is running Ubuntu Server 18.04 Bionic, CLI only. It has a wired
connection to a DHCP-enabled home router initially, but will use wireless
internet after this in finished</p>
<h1>Find and Start the Wireless Device</h1>
<pre><code class="language-bash">ip link
</code></pre>
<p>Mine was called <code>wlp2s0</code>. Start it:</p>
<pre><code class="language-bash">ip link set dev wlp2s0 up
</code></pre>
<hr>
<h1>Download &#x26; Install wireless software</h1>
<p>Ubuntu server doesn't ship with the required packages to connect to WiFi.</p>
<p>From another Ubuntu server that <strong>does</strong> have internet, plug in a USB stick
and mount it. This example assumes it's mounted to /mnt.</p>
<p>I'm pretty sure that it can connect to WEP without this, and its just the
newer WPA2 networks that basically everyone is using that need this.</p>
<pre><code class="language-bash"># Delete anything currently in the apt cache
apt-get clean

# building some temp package lists, drop them in ~ or wherever
cd ~

# use apt-rdepends to get the dependencies
apt-get install apt-rdepends

# find deps for wireless-tools
apt-rdepends wireless-tools 2>/dev/null | grep "Depends: " | awk '{print $2}' | sort | uniq > packages1
echo wireless-tools >> packages1

# find deps for wpasupplicant
apt-rdepends wpasupplicant 2>/dev/null | grep "Depends: " | awk '{print $2}' | sort | uniq > packages2
echo wpasupplicant >> packages2
cat packages1 packages2 | sort | uniq > packages

# download the debs
cd /var/cache/apt/archives
cat ~/packages | while read p; do echo $p; apt-get download $p; done

# Copy the files
mkdir -p /mnt/debs
cp /var/cache/apt/archives/*.deb /mnt/debs
umount /mnt
</code></pre>
<p>Now remove the USB drive from that system and plug it into the offiline one.</p>
<pre><code class="language-bash"># mount the usb drive
mount /dev/sdb1 /mnt

# move the files to your cache directory
cp /mnt/debs/* /var/cache/apt/archives/

# Install the packages
apt-get install wireless-tools wpasupplicant
</code></pre>
<h1>Scan for SSIDs</h1>
<p>The <code>iwlist</code> command can also give you other information about the network if
you don't pipe its output to grep, but it's pretty verbose.</p>
<pre><code class="language-bash">iwlist wlp2s0 scanning | grep -ie ssid
</code></pre>
<h1>Join the WiFi Network with Netplan</h1>
<p>You can use various commands to interactively connect to the network, but I
want this connection to come up with the NUC. Netplan is the new tool used to
configure networks since Ubuntu's Bionic stable release. Here's the netplan
config I used. You can see the wired connection in there too, it doesn't need
to be there once this is finished.</p>
<p>Be sure to replace "<code>MySSID</code>" and "<code>My Password</code>" with your own.</p>
<p><code>vi /etc/netplan/01-netcfg.yaml</code></p>
<pre><code>network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      dhcp4: yes
  wifis:
    wlp2s0:
      dhcp4: yes
      access-points:
        "MySSID":
          password: "My Password"
</code></pre>
<p>Then apply the changes.</p>
<pre><code>netplan try
</code></pre>
<p>You should have an IP address now in <code>ifconfig</code>. For some reason I didn't get
one right away, so I forced the DHCP request like this:</p>
<pre><code>dhclient wlp2s0 -v
</code></pre>
<p>After that, you can connect to the wireless IP and don't need the wired one.</p>
<h1>Reference Links</h1>
<ul>
<li><a href="https://askubuntu.com/questions/138472/how-do-i-connect-to-a-wpa-wifi-network-using-the-command-line">AskUbuntu post about wpasupplicant</a></li>
<li><a href="https://ubuntuforums.org/showthread.php?t=2392154">Ubuntuforums.org netplan post</a></li>
</ul>


Kyle Pericak

"It works in my environment"

Categories

Tags