Raspi as a router
=================


Assuming Ubuntu LTS, Here are the main steps.

Setup
-----

* eth0 connected to laptop
* wlan0 connected to internet (via home network) either static IP or dynamic

Steps
-----

* configure a static IP in /etc/netplan for the local raspi network. say 192.168.10.1/24
* use dnsmasq as a DHCP Server, to provide a dynamic IP address, and a default gateway
* enable IPv4 forwarding
* MASQUERADE


Tools to install
----------------

.. code-block:: bash

    sudo apt install dnsmasq # for DHCP server
    sudo apt install iptables-persistent # for IPv4 and IPv6 Persistent config


Code
----

First place a config file in /etc/netplan

.. code-block:: yaml

    network:
      version: 2
      ethernets:
        eth0:
          dhcp4: false
          optional: false
          addresses:
            - 192.168.10.1/24
      wifis:
        wlan0:
          access-points:
            starport:
              password: 1uEu@xjajo@AynX
          addresses:
            - 2601:0181:c400:121b::bebe/64
            - fde8:b060:bd2c:0001::bebe/64
            - 2601:0181:c400:121b:b060:bd2c:0001:bebe/64
            - 192.168.0.21/24
          dhcp4: false
          dhcp6: false
          gateway4: 192.168.0.1
          gateway6: "2601:181:C400:121B:1E3B:F3FF:FED2:6309"
          nameservers:
            addresses: [192.168.0.1]    # DNS Server IP addresses.

.. caution::
    Since the wlan0 wifi is using a static IP, a default gateway must be provided


Second dnsmasq should bind to a specific interface, otherwise it conflicts with systemd-resolv

.. code-block:: bash

    bind-interfaces # to bind to specific interfaces rather than all available interfaces
    interface=eth0 # specify the interface to bind to
    dhcp-range=192.168.10.100,192.168.10.120,255.255.255.0,24h # DHCP server config


Third, enable IPv4 forwarding.

* uncomment ``net.ipv4.ip_forward=1`` for the next reboot
* run ``sudo sysctl -w net.ipv4.ip_forward=1`` to enable in this session


Forth, enable NAT MASQUERADE

* ``sudo iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE`` to enable right away
* ``sudo /sbin/iptables-save && sudo /sbin/ip6tables-save`` to persist iptables settings