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I have the following topology:

Topology

I intend to build this network with the PC acting as a DHCP server and multiple IP-enabled custom development boards connected to the switch and some connected to each other for network redundancy. By design, each dev board has two Ethernet ports and retransmits data received on a port to another.

I am worried that the connections between the dev boards could generate loops.

Can this topology be used without existing the risk of loops appearing? How? Does the switch automatically recognize the connected devices (MACs) and avoids loops?

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Switch uses Layer 2 Spanning Tree Protocol to ensures a loop free topology for any bridged Ethernet network. So if yours IOT device will forward bridge protocol data unit (BPDU) accross, switch will maintain loop free topology. BPDU are transsmited accross local network to detect loops in network topologies. If BPDU won't be forwarded you can possibly have a loop. But effect of STP could be something like on this picture.enter image description here

So two IOT boards would be able only to talk with DHCP server thru another IOT board.

  • Thank you! Since all data received on one port is retransmitted on the other it means the devices will forward BPDUs. – Cristian M Feb 12 '17 at 11:04
  • Thanks again for the edited answer. That is the intended operation. Then, if the connection becomes unavailable, the switch will use the previously unused connection (that marked with red x). – Cristian M Feb 12 '17 at 11:17
  • @CristianM, BPDUs use a special multicast MAC address that the IEEE reserves and has written into the standard that ethernet will not send traffic destined to that address to another interface. Are you absolutely sure that the BPDUs will travel in a circle? – Ron Maupin Feb 12 '17 at 16:14
  • @RonMaupin The idea was to basically create a bus so that a packet can reach its destination. Can you give me an advice on how to correctly implement this topology? The devices are MSP controllers with RTOS TCP-IP stack. – Cristian M Feb 13 '17 at 18:33
  • @RonMaupin And if a link would break (physical problem) the communication could still be done using a device as a relay, retransmitting the messages. – Cristian M Feb 13 '17 at 18:41

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