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This seems to be the simplest pattern for getting remote access to your LAN. It doesn't require access to the LAN's router or have some of the pitfalls of bridging. This requires a Linux PC or VM, something that runs iptables, on your LAN. A raspberrypi works. This is a NAT/Masquerade setup.

Possible Disadvantages:

  • No broadcast/multicast across networks (but the mobile OS's don't allow this anyways).

  • Can't initiate connections from the LAN to an external ZeroTier client.

Summary

  • Install ZeroTier

  • Add a managed route to the ZeroTier network (at my.zerotier.com)

  • Enable IP Forwarding

  • Configure iptables

Required information

For Example:

Info

Example

Shorthand Name Below

ZeroTier Network ID

d5e04297a19bbd70

$NETWORK_ID

ZeroTier Interface Name

zt7nnig26

$ZT_IFACE

Physical Interface Name

eth0

$PHY_IFACE

ZeroTier subnet

172.27.0.0/16

 

Physical subnet

192.168.100.0/24

$PHY_SUB

ZeroTier IP Address of "Router"

172.27.0.1

$ZT_ADDR

Install ZeroTier

https://www.zerotier.com/download/

sudo zerotier-cli join $NETWORK_ID
sudo zerotier-cli listnetworks

Authorize it at my.zerotier.com/network/$NETWORK_ID

The listnetworks output has the ZeroTier Interface name under <dev>

Configure the ZeroTier managed route

At my.zerotier.com/network/$NETWORK_ID -> Settings -> Managed Routes

This adds another route to every device joined to the ZeroTier network.

Destination

(Via)

$PHY_SUB

$ZT_ADDR

For example:

Destination

(Via)

192.168.100.0/23

172.27.0.1

Configure the destination route as slightly larger than the actual physical subnet, here /23 instead of /24 (a smaller number is a bigger subnet in this notation) This makes devices that are on both the physical and the ZeroTier network prefer the physical connection.

Enable IP forwarding

This can vary depending on linux distribution. Typically:

Edit /etc/sysctl.conf to uncomment net.ipv4.ip_forward. This enables forwarding at boot.

To enable it now

sudo sysctl -w net.ipv4.ip_forward=1

Configure iptables

Assign some shell variables (personalize these)

PHY_IFACE=eth0; ZT_IFACE=zt7nnig26

Add rules to iptables

sudo iptables -t nat -A POSTROUTING -o $PHY_IFACE -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o $ZT_IFACE -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i $ZT_IFACE -o $PHY_IFACE -j ACCEPT

Save iptables rules for next boot

sudo apt install iptables-persistent
sudo bash -c iptables-save > /etc/iptables/rules.v4

Test!

  • Turn off wifi on your phone

  • Join it to the zerotier network, authorize it

  • Try to access something on the physical LAN

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