This section covers some troubleshooting guidance for forming the network. The border router is responsible for forming the network and allowing nodes to join the network. The first step when initially setting up the network is to follow the guidance in Form a network. When adding a device to the network, always make sure the border router and the node share the same parameters as described in Add devices to an existing network.

Can’t communicate after reboot

After a restart, the border router will restore its IPv6 neighbor caches and its RPL routes from storage. However, it must reacquire its neighbors' frequency hopping timing information. This information will be restored once the border router receives a PAN configuration or a data frame from each neighbor. This can take some time depending on your network configuration. See Tune the network for information about tuning your network.

To be able to send data frames for a node up to the border router, the border router’s neighbor nodes must have updated frequency timing information as well.

LFN devices are a special case; they expect to receive an LFN Time Sync (LTS) Frame every so often. After a restore, since frequency hopping timing information is not available to send an LTS, LFNs will consider their parent no longer present and will perform a full join procedure.

Nodes do not discover the network

If nodes do not proceed past scanning or attempt authentication:

  • Confirm that Channel Plan ID, PHY Operating Mode ID, and Network name match between the nodes and the border router as described in Form a network and Add devices to an existing network.

  • Check that the broadcast schedule is not too sparse.

    See Tune the network for information about tuning your network.

  • Excessively long Broadcast Intervals or very short Broadcast Dwell Intervals can make discovery unreliable. Move a node closer to the border router or add an intermediate router to test.

Authentication or authorization fails

If nodes discover the network but fail during 802.1X EAP authentication or do not receive keys:

  • Verify the node has valid credentials and is authorized to join this network. See Secure the network for more information.

  • Ensure the border router can reach the authentication server and that firewall rules permit EAP and RADIUS traffic if used. This should be the case by default.

  • Confirm system time is correct on the border router. Incorrect time can cause certificate validation failures.

  • If you recently rotated keys, allow time for the new group key index to propagate and avoid rotating more quickly than nodes can join.

Nodes see the network but never become reachable

If authentication succeeds but nodes do not pass IPv6 traffic:

  • Verify that an IPv6 prefix is configured and advertised into the Wi‑SUN mesh.

  • Confirm that RPL is running and DIOs are being sent after network formation.

  • Check neighbor and route tables on the border router.

Broadcast schedule too tight or too loose

If joins are extremely slow or management traffic appears starved, decrease Broadcast Interval or increase Broadcast Dwell Interval to allocate more airtime to control traffic. If Broadcast Interval is too long, discovery and configuration can take minutes. If Async Fragment Duration is too small, multi‑fragment management messages can spill across many intervals. See Tune the network for information about tuning your network.

Duplicate or overlapping networks

If nodes join the wrong network or flip between networks in the same area:

  • Ensure the network name is unique to your deployment.

  • Avoid running multiple independent border routers that advertise the same network name unless they are intentionally part of the same administrative domain and backend.

LFN join and sync issues

If LFNs take excessively long to join or drop after the border router restarts:

  • Verify LFN Broadcast Interval and LFN Broadcast Sync Period are configured and appropriate for the LFN class in use.

  • Consider temporarily shortening the LFN intervals during mass onboarding and restoring longer intervals after stabilization.

After a reboot, expect LFNs to re‑authenticate if they miss LTS windows.

Join storms and congestion

If large fleets take a long time to converge and many nodes back off or time out:

  • Stage device power‑up in batches.

  • Increase broadcast capacity temporarily by shortening the Broadcast Interval and increasing Broadcast Dwell Interval.

  • After the fleet has joined, restore normal settings to free airtime for data.