Tunnels and cross-links both connect two nodes together, so they are the same in that respect. However, they do it in very different ways.
**Tunnels** are a simple to use, all in one feature, which operates over your regular Internet to connect two AREDN |trade| nodes. There is a bit of configuration information to exchange, but it is all fairly easy to set up. Tunnels *only work* over your **WAN** connection, you use the IP address given by the server, and there is very little else to configure.
**Cross-links**, on the other hand, are much more basic and flexible. The configuration lets you choose IP addresses yourself, as well as setting a VLAN and *port* on which xlink traffic leaves the device. The IP addresses let the system route the data (OLSR works at layer 3 so every interface needs an IP address), but unlike the tunnel you can set these addresses any way you desire. You choose any unused VLAN number yourself, and the *port* sets how you want the data to be physically sent into or out of the node. How the data is moved to the peer device is not defined in any way, and deliberately so. Maybe you want to connect that *port* directly to a non-AREDN |trade| PtP radio. Maybe you feed it into a switch then use some other tunneling technology to get it where it needs to go. Maybe it is just a bit of Ethernet cable. It is entirely up to you. Personally, I use tunnels to connect nodes over the Internet, but I use xlinks to connect nodes over Point-to-Point radios which are not running AREDN |trade| firmware.
You can use either a *Mikrotik hAP ac2* or *ac3* as the AREDN |trade| device on each end of the cross-link. Navigate to the **Administration > Advanced Network** page of the node on one side of the link. To add a cross-link click the *plus* icon, enter an unused VLAN number for the link, an IP address for the near-side radio, an IP address for the far-side radio, a weighting factor, and the available port to which the near-side radio is connected on your node. The *Weight* will be used by `OLSR <https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol>`_ to determine the best route for AREDN |trade| traffic.
In this example we chose VLAN ``20`` because it is not in use anywhere else on our network. We assigned an *IP Address* of ``172.16.1.1`` for the this node, and we assigned ``172.16.1.2`` as the *Peer Address* for the node on the other side of the link. The xlink knows nothing about the details or configuration of the PtP radios, or their IP addresses. The *Weight* is set to ``1`` which is the same weight as would be used by a tunnel connection, but this can be increased if you want the cross-link to be chosen at a lower priority for routing traffic on the mesh. *Port*``3`` was chosen because it is an open port on this device. After entering your values, click *Save Changes* to save the new cross-link information. Now you can cable your near-side PtP device to port 3 on your AREDN |trade| node.
Next, open the **Administration > Advanced Network** page on the node for the other side of the PtP link. Set the *IP Address* for this node to ``172.16.1.2`` and the *Peer Address* for the node on the other side of the link to ``172.16.1.1``. The *Weight* is set to ``1`` which is the same weight as would be used by a tunnel connection, but this can be increased if you want the cross-link to be chosen at a lower priority for routing traffic on the mesh. In our example we are setting the *Port* to ``4`` because it is an open port on this device. After entering your values, click *Save Changes* to save the cross-link configuration for this side of the PtP link. Now you can cable your far-side PtP device to port 4 on your AREDN |trade| node.
How data is moved between the peer devices is not restricted or defined. There are many types of vendor-specific Point-to-Point products that can be used to establish an AREDN |trade| cross-link. Refer to your manufacturer's documentation for the best way to ensure that network packets can be successfully transferred between the two endpoint devices. The easiest way to accomplish this is to bridge the traffic directly between the peer devices.
