Connecting two managed switches together (RSTP and loopback prevention)

Connecting two managed switches together (RSTP and loopback prevention)
Connecting two managed switches together (RSTP and loopback prevention)
2019-02-19 13:20:37

Hi

I connected two switches together a "T1600G-52TS" and "TP-Link SG2216". Both of them are connected to the last port on both switches (I don't have SFP yet, no money for that at the moment).

 

First question: 

As I understand if i set "Spaning Tree protocol" to DISABLED but "Loopback Detection" ENABLED, does it mean that I don't need STP ? I've read a lot on internet, that simple "Loopback Detection" only works if you accidentally connect two ports of the same switch together. It will not work if you connect a unmanaged switch to the main managed switch and create a loop on that "dumb" switch. Is that true ? This really confuses me, because I really don't know the difference.

 

Second question:

If I need RSTP in this scenario, what are the proper RSTP settings for connecting theese switches together. I have red the tutorial https://www.tp-link.com/us/faq-942.html, but I don't know if this is the right one for my case. 

 

What I wan't to do:

- protect the network if someone creates a loop on switch  "T1600G-52TS" or/and "TP-Link SG2216"

- protect the network if someone connects a unmanaged switch ant create a loop on that switch (so only the dumb switch gets stuck, not the whole network).

- protect the newtork if somone creates a loop between two of those main managed switches

 

I would be very gratefull if anyone with experience can guide me :)

 

 

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5 Replies
Re:Connecting two managed switches together (RSTP and loopback prevention)
2019-02-21 02:09:53

lukas85 wrote

Hi

I connected two switches together a "T1600G-52TS" and "TP-Link SG2216". Both of them are connected to the last port on both switches (I don't have SFP yet, no money for that at the moment).

 

First question: 

As I understand if i set "Spaning Tree protocol" to DISABLED but "Loopback Detection" ENABLED, does it mean that I don't need STP ? I've read a lot on internet, that simple "Loopback Detection" only works if you accidentally connect two ports of the same switch together. It will not work if you connect a unmanaged switch to the main managed switch and create a loop on that "dumb" switch. Is that true ? This really confuses me, because I really don't know the difference.

 

Second question:

If I need RSTP in this scenario, what are the proper RSTP settings for connecting theese switches together. I have red the tutorial https://www.tp-link.com/us/faq-942.html, but I don't know if this is the right one for my case. 

 

What I wan't to do:

- protect the network if someone creates a loop on switch  "T1600G-52TS" or/and "TP-Link SG2216"

- protect the network if someone connects a unmanaged switch ant create a loop on that switch (so only the dumb switch gets stuck, not the whole network).

- protect the newtork if somone creates a loop between two of those main managed switches

 

I would be very gratefull if anyone with experience can guide me :)

 

 

 

Hi lukas85

 

Spanning tree is used for the loop topology. For example, you have three managed switches that support spanning tree and they are connected each other as a loop.

A<--->B<--->C<--->A

When you use spanning tree, suppose that switch A become the root bridge, then the connection between B and C will be blocked. The topology will become B<--->A<--->C.

At this moment, suppose that the connection between A and B has issue and become disconnected, then the spanning tree will re-negotiate. The topology will become A<--->C<--->B.

So the spanning tree can prevent the loop and has the rebundant effect. A and B and C connect each other as a loop, if there is one connected down, they still can work normally. Please note that all switches need to support spanning tree, then they can negotiate with each other.

 

Loopback prevention is send the detection packets to detect the loop, if it receive the same packets that it sends out, it means that there is loop, switch will block the port.

 

So you can configure the loopback prevetion for the ports connected to unmanaged switch. And configured spanning tree for the ports between managed switch. 

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Re:Re:Connecting two managed switches together (RSTP and loopback prevention)
2019-02-25 11:01:01

Ok, but what will happen if I connect an unmanaged switch to the main switch and create a loop on that unmanaged switch.  Will it cause a network shutdown or the port where the unmanaged switch is connected will be blocked ?

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Re:Re:Re:Connecting two managed switches together (RSTP and loopback prevention)
2019-02-26 05:59:35

lukas85 wrote

Ok, but what will happen if I connect an unmanaged switch to the main switch and create a loop on that unmanaged switch.  Will it cause a network shutdown or the port where the unmanaged switch is connected will be blocked ?

 

Hi lukas85

 

If you use loopback detection for the ports connected to unmanaged switch, you can set up "alert" or "port based" or "VLAN based" operation mode for loopback detection.

 

Alert
The Loop Status will display if there is a loop detected on the corresponding port.
 
Port Based
The switch will display an alert and block the corresponding port when a loop is detected.
 
VLAN Based
The switch will display an alert and block the corresponding VLAN when a loop is detected.
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Re:Re:Re:Connecting two managed switches together (RSTP and loopback prevention)
2020-06-05 18:27:31

@Anderson 

 

Good affternoon

 

Can I use the STP and LDP protocol on the same port? Is there a conflict?

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Re:Re:Re:Connecting two managed switches together (RSTP and loopback prevention)
2020-06-17 03:43:50

@Agarcia 

 

Do you mean use STP and LLDP protocol on the same port? Yes, you can. 

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