Navigating RF Interference in the 5.8GHz Band for WISPs: The Critical Role of OOB Management

Wireless Internet Service Providers (WISPs) operating in the 5.8 GHz band frequently encounter challenges with radio frequency (RF) interference. This interference can degrade network performance, reduce throughput, and in severe cases, disrupt connectivity. Given the crowded nature of the 5.8 GHz band, it's essential for WISPs to implement strategies that not only mitigate interference but also ensure reliable network management. One effective approach is the use of Out-Of-Band (OOB) management, particularly through LTE connections, to maintain access to high sites even when primary links are unusable.

The Value of LTE for OOB Management

Integrating an LTE device connected to a MikroTik router at the high site provides a robust OOB management solution when coverage allows it. This setup is invaluable for situations where adjustments to the frequency of backbone links are necessary. Such changes, while aimed at mitigating RF interference, can sometimes lead to lost connectivity to the high site. In worst-case scenarios, the link may fail to re-establish, leaving the site unreachable.

An LTE-based OOB management pathway ensures that administrators can access the high site, make necessary adjustments, or restore configurations without physical intervention. This is particularly critical in remote or difficult-to-access locations.

Configuring MikroTik for OOB Management via LTE

Example: Static Route for VPN Over LTE

To configure a MikroTik router for OOB management with an LTE connection, you can set up a VPN that routes through the LTE. This ensures that even if the primary connection fails, the VPN remains accessible as a management channel. Here's how you might configure a static route to force a VPN connection over LTE, assuming the LTE router has the IP address 192.168.254.1:

/ip address add address=192.168.254.2/24 interface=ether5-LTE comment="LTE IP address"
/ip firewall nat add chain=srcnat out-interface=ether5-LTE action=masquerade
/ip route add dst-address=<VPN_Server_IP> gateway=192.168.254.1 comment="Static route for VPN over LTE"

Replace <VPN_Server_IP> with the IP address of your VPN server. This setup directs all VPN traffic to use the LTE connection, ensuring it remains active even if the main link is down.

Alternative: Enabling Inbound Connections via LTE with DMZ

If you prefer not to use a VPN, you can configure the MikroTik router to allow inbound connections from the LTE by setting the MikroTik as a DMZ target. This requires a default route, input and output mangle rules, and a separate DMZ setup. Additionally, you'll need to ensure the public IP address used for network administration is allowed through the control plane firewall. Here's a basic configuration example:

/ip address add address=192.168.254.2/24 interface=ether5-LTE comment="LTE IP address"
/ip firewall nat add chain=srcnat out-interface=ether5-LTE action=masquerade
/ip firewall mangle add chain=prerouting in-interface=ether5-LTE action=mark-connection new-connection-mark=LTE
/ip firewall mangle add chain=prerouting connection-mark=LTE action=mark-routing new-routing-mark=LTE
/ip route add dst-address=0.0.0.0/0 gateway=192.168.254.1 routing-mark=LTE comment="Route for admin network over LTE"

In this configuration, a new routing mark called "LTE" is created, and a default route is added to use this routing mark. This ensures that traffic coming in from the LTE interface is routed back out through the LTE interface.

Remember to configure the LTE device to use the MikroTik (192.168.254.1) as its DMZ target. This allows inbound connections to the LTE device to be forwarded to the MikroTik, ensuring that administrators can access the high site even when the primary link is down.

The downside of this approach is that it exposes the MikroTik to the public internet, which may not be desirable from a security standpoint. However, with proper firewall rules and security measures, this risk can be mitigated.

Another consideration is the use of dynamic DNS services (on the LTE device) to ensure that the public IP address of the LTE connection is always known, even if it changes.

Conclusion

RF interference in the 5.8 GHz band is an ongoing challenge for WISPs, but with the right strategies and configurations, it's a manageable one. Implementing LTE-based OOB management ensures that network administrators can maintain access to high sites, even when primary connections are too unstable to carry management traffic.