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IP Passthrough issues on CBRS gateways

A general note for everyone…during device testing I’ve seen a number of gateway vendors do strange things with IP addressing on WAN interfaces of CBRS modems. It can happen when using “Passthrough mode” which maps the WAN IP directly to a single host (like an IP camera or IoT sensor you may need to connect to from the LAN).

If you’re extending LAN subnets into the CBRS network it is possible the gateway will create a /30 using host IPs already in use on your subnet, less than ideal.

Example, using IP camera connected to CBRS gateway;

  • Celona platform configured with a custom, external IP domain connected to subnet 10.45.0.0/24 on the LAN.

  • CBRS gateway connects, and receives 10.45.0.125/24 as it’s allocated IP.

  • CBRS Gateway passes 10.45.0.125/30 to the IP Camera with default gateway IP of 10.45.0.126. Resulting in no connectivity.

  • Furthermore, 10.45.0.126 may already be an active host in the subnet.

The fix is to set the subnet and default gateway statically in the WAN interface of the CBRS gateway.

Historically, these LTE gateways have been deployed on MNO networks, where these IP addressing issues do not exist. We have shared our findings with a number of vendors and expect fixes to be rolled out in subsequent firmware releases.

In the meantime, watch out for this on your network.

UPDATE from this weeks testing across the company.

We’ve seen issues with features like DHCP relay to LAN hosts behind Sierra RV55. The team at Sierra helped us identify the issue and apply a patch in a matter of days :white_check_mark: Great work folks!

We have also seen the gateway and subnet issues appear when Cradlepoint gateways are in NAT mode. The same fix applies. Enter the Connection settings for the modem in question, manually set gateway and subnet. Thanks also to the whole team at Cradlepoint who are always going above and beyond to support CBRS networks.