Spanning tree for 20+ devices

[stzeljko]

Hello guys, would be thankfull if you can assist me with next thing.

Network is consisting of 4 ''branches'' which all need to be in same vlan, and every branch need to close in circle with main L3 switch. There are two large (~15 industrial L2 switches) and two small (~5 industrial L2 switches). They are all connected to L3 switch in stack (2x switches). All of them should be able to see each other.

When I configure rstp with 30+ devices, after shutdown one of devices, recalculation of route is taking to much time.

In attachment is Cisco pt scheme.

What do you suggest?

Thanks, best regards.

[David Ruess · Accepted solution]

Hello,

Can you be a little more clear on the question. You says recalculation of route takes too much time? Do you mean the routes of the packets at L2? The convergence of switches due to spanning tree?

A couple of statements:

1.) Assuming the L3 switch is the termination of the VLANs make sure it is the root with the command "spanning-tree vlan 274 root primary"

2.) If there are devices connected to the end switches such as printers and PCs, then configure the edge ports for "spanning-tree portfast" This does not generate a TCN every time a port goes up or down. 

3.) Configure "spanning-tree uplinkfast" on all branch L2 switches. This allows the alternate port (backup route of L2 packets) to transition to forwarding packets faster.

Hope that helps

-David

[stzeljko · Accepted solution]

Hello David, thank you for fast reply.

You says recalculation of route takes too much time? - After I shut down port on main link, ping from one pc to another branch's pc is not working, and they are connected through redundant link.

All switches must be in mgmt vlan 200, placed in 4 branches connected separately in L3 stack switch (2xswitches in stack)

(1 branch= 15 deveices, 2 branch= 20 devices, 3 branch= 5 devices, 4 branch = 3 devices)

1.) 2.)3.) OK

[David Ruess]

Only 2 of your branches have redundant links. If you shut down the main link on either of the other branches you will lose all connectivity to that branch and devices wont be able to ping. Add in another link for the branches with only one link to the L3 switch to provide redundancy. Also let me know if those commands helped at all.

-David

[stzeljko]

Hello David, I am using Cisco pt so I don't have command "spanning-tree uplinkfast".

On jpg attachment you can se number of switches (+- 2 because some switches would be from other company but same vlan). I think I found some solutions combining your and Flavio answers. 

Thanks, br.

[Flavio Miranda]

Hi

I can not try to help you without trying to give you another direction. The requirement is all hosts need to "see" each other but if you have a Layer 3 switch in between, why dont you create Inter vlan routing and use different networks for each site instead putting all og them in the same vlan? 

You might know that 40 switches on the same vlan will be a massive broadcast domain, right? 

With Inter vlan routing you can broake the broadcast domain and still maintain the connectivivy between hosts. 

[stzeljko]

Hello Flavio, thanks for fast reply.

Yes you understand very well, and I agree that will be massive broadcast domain, my idea was for every branch different subnet and vlan. But we already get scheme as I said in post ''which all need to be in same vlan''.

That is confusing me, only thing I know is that this vlan 200 is mgmt vlan, and we have different vlans for ''normal'' and video traffic for edge devices connected to switches, but they are propotionally placed.

[Flavio Miranda · Accepted solution]

Well, if we are talking about management only then I´d say is less critical. For management, we are basically talking about one vlan and 40 hosts. Also, management traffic is not much. 

 About the problem you faced, was it in real world or on your lab?  Are you using RSTP or standard STP ?

[stzeljko]

Hello Flavio, jep, that will only be mgmt vlan, we have other vlans for other traffic.

I was using Cisco pt application, rstp, but I haven't take per-vlan STP because our L2 industrial switches in prodcution don't have per vlan rstp.

I think I found some solutions combining your and David answers.

Thanks, br.

[David Ruess]

Glad you found a solution with the answered provided. Yes, unfortunately packet tracer has manatee limitations, spanning tree being one of them as far as commands and functionality.

Please make sure to mark this as solved (you can mark more than one answer as a fix) so the community can use this post in the future.

-David