As per the article on choosing a cellular plan, we advise monitoring your cellular usage to account for your network and unique usage patterns. This article provides general guidance but is not a substitute for real world testing.
Points of note:
- Cellular carriers typically charge for both inbound and outbound network traffic, so the numbers in this article are for combined inbound and outbound usage and are given in megabytes (MB).
- If your Opengear device has a public cellular IP, even when an access attempt is blocked by the Opengear device's firewall, the inbound data used still counts against your quota. Nevertheless, enabling security features such as Brute Force Protection can discourage attack attempts (i.e. the perpetrator moves on in search of an "easy target") that would otherwise use data.
- Always configure cellular data usage alerts to avoid overage charges.
The optional Modem Watchdog will typically use 10 – 50MB/month in probe traffic. This is configurable as described in this article.
Connection to a Lighthouse management server will use 200MB/month. Ensure Monitor Managed Devices is unchecked (this is the default) when enrolling the console server, to avoid polled monitoring.
Polled monitoring services such as Nagios or Solarwinds SNMP may use many 100s of MB/month. If these are to be used over cellular, take care to tune periods and limit the data points (e.g. remote checks or OIDs) requested in the the monitoring server configuration, to manage data use.
Event monitoring alerts such as SMTP email, Nagios NSCA alerts or SNMP traps typically use very little data (less than 0.1MB per event).
If explicitly configured, IPsec Dead Peer Detection and OpenVPN ping/keepalives may use 10s of MB/month.
Tunneling traffic tends to add between 5% and 10% data overhead.
An SSH session to a console will typically only use a small amount of data, less than 1MB/session.
Note that a 9600bps console constantly transmitting data over SSH at "full blast" may consume in the order of 12MB/hour, however this is not a typical scenario. Cellular data is not used when there in no network connection (e.g. SSH) to a console.
An HTTPS browser session to the Opengear web UI will typically only use a moderate amount of data, 1 to 2MB/session.
However certain tasks such as backing up configuration or viewing port logs may use multiple MBs. Upgrading firmware may use 20MB+.
SMS messages sent directly by the cellular modem (not via an SMTP gateway) typically do not count towards your data usage, but may be separately billable.
An effective way to reduce data usage is to disable cellular when it's not required. Your Opengear device can do this automatically using failover:
- Click System -> IP -> Network Interface
- Scroll down to Failover
- Set Failover Interface to Internal Cellular Modem
- Enter a Primary and Secondary Probe Address
- Click Apply
Note: The trade-off on using failover is that it introduces a significant "moving part" into your network configuration. Therefore it is critical that you take measures to ensure the cellular connection will become available when it's needed:
- Choose appropriate probe addresses that indicate that primary inbound access has become unavailable
- Test thoroughly by simulating failover scenarios, e.g. shutdown upstream interfaces, block pings to the probe addresses
- Perform or automate regular maintenance tests to ensure your cellular connection is operating as expected
If your cellular plan supports SMS, as a backup consider using SMS commands to manually start and stop the cellular connection.
Refer to this article for details on available failover modes.