If I put the hub in between the switches (four or five ethernet switches), the spanning tree will not work. The loop would be created. Grateful if you could enlighten me.
Depends how you connect it up ie.
sw1 -> sw2 -> hub -> sw3 -> sw4
there is no layer 2 loop there so you will be fine. So using a hub does not necessarily create a L2 loop. However a hub simply forwards a packet out of all it's interfaces except the one it received it on. So yes you could create a loop with a hub but you could also create a loop with L2 switches.
However most hubs don't run STP so yes it is easier to create a loop and this loop will not be blocked on the hub.
if you connect 4 or 5 switches to hub ports please check the duplex and speed settings on switch ports:
an hub can only work in half duplex mode and cannot accomodate different speeds: that is user at 100 Mbps see only other user at 100 Mbps and users at 10 Mbps can only see other 10 Mbps users (at least this is what I see in my home hub)
if duplex is harcoded to full on switch ports it is a problem.
Besides this, each switch should see the BDPU sent by other ones and only one port should be elected as designated port in segment and all the other ones should be in blocking.
Verify also that the device is really an hub and not a switch: you can check this using STP bdpu guard on a Cisco switch.
Verify also that your switch ports are not using the dangerous STP bpdu filter enabled at port level this would lead to a loop.
Verify also if STP portfast is enabled on switch ports this can enough to cause the loop.
Using ports without portfast and no bpdu filter and with no duplex/speed issues you should be able to avoid the loop (not guaranteed but likely)
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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