Reference9:Interfaces/ETH/RSTP

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There are other versions of this article: Reference8 | Reference9 (this version)

The RSTP function is provided for devices connected to a redundant bridged network when a device must stay operational even if a network port or a bridge in the network fails. If RSTP is enabled ETH0 is assumed to be the the primary port and ETH1 the backup port. RSTP packets are sent over both ports. From received RSTP packets it is learned which port shall be used for data traffic. If it is ETH0 the IP stack runs as configured over this port. If it is ETH1 the IP stack is moved to ETH1 and the new IP-address to MAC-address binding is broadcasted over the network. The port to be used for data traffic may change whenever the network topology changes, i.e. when a link between bridges goes down or up or a bridge is added. On each such change the IP stack is moved to the selected port without disruption of data traffic.

Before RSTP can be enabled the following preconditions must be met:

  • The device must be connected to external power (even when both ports are PoE powered switching from one PoE source to the other may restart the device).
  • The bridges in the network should support RSTP
  • The device ports should be connected to RSTP enabled bridge ports
  • The device ports should be connected to different bridges
  • IP4/ETH0/IP must be completely configured for a fixed IP address
  • IP4/ETH0/IP checkmarks must be unchecked
  • IP4/ETH1/IP Disable must be checked
  • DHCP must be disabled on both ports
  • VLAN must not be enabled on any port
  • PPPoE must not be run through either port


Note: When using Gateways IPxx10/xx11/11xx that don't have external PSU we could face the problem described in the first point that the device "may" restart during the switch, however if the device receives PoE with the same voltage (similar switch) value on both ports (ETH0/ETH1) it will not restart during the switch.

A restart can happen if the first POE source supplies a higher voltage as the second so that the load of the second POE source is so low the second POE is switched off. When switching from the first to the second POE source the second needs to be turned on first. The IPxx10/xx11/11xx Gateways show the power sources at the web UI, also most POE switches provide an LED indication or a web UI to check is power is sourced to a POE port.


Enable: Enables the RSTP function.
Trace Actions: Trace events triggering RSTP state machine actions and the actions performed by the state machines.
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