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Maximum number of SF250 switches on a LAN

hallio
Beginner
Beginner

I have a project where a nurse call system in a UK hospital will be connected to 24 port SF250 switches. Due to the size of the project i will potentially be using up to 90 of these switches split into multiple VLANs with RSTP enabled.

 

does anyone for see any issues or have had any experience of using this switch on this scale?   

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balaji.bandi
VIP Community Legend VIP Community Legend
VIP Community Legend

Personally i do not belive there any Limitation here, Make sure you plan the network in planned manner, Not to Loop them

 

example : 3 Tier Model network, where possible to get advantage and effective way, Do not make any Daise chain, if the chain breaks end of all device can not reach  top level  network.

 

so split them in Group make redudency in the network for alternative path always.

 

Note : Since you mentioned Hospital, there is a Critical care always keep that in mind, so suggest to Look for Cat 1K or Cat 9200 switch where possible - they are robust and seen years of uptime with out any issue.

 

BB

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5 Replies 5

balaji.bandi
VIP Community Legend VIP Community Legend
VIP Community Legend

Personally i do not belive there any Limitation here, Make sure you plan the network in planned manner, Not to Loop them

 

example : 3 Tier Model network, where possible to get advantage and effective way, Do not make any Daise chain, if the chain breaks end of all device can not reach  top level  network.

 

so split them in Group make redudency in the network for alternative path always.

 

Note : Since you mentioned Hospital, there is a Critical care always keep that in mind, so suggest to Look for Cat 1K or Cat 9200 switch where possible - they are robust and seen years of uptime with out any issue.

 

BB

***** Rate All Helpful Responses *****

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Martin Aleksandrov
Cisco Employee
Cisco Employee

Hello hallio,

 

There is a limitation. Please do not implement this scenario! Having connected 90 cascaded devices Sx250/350/550 will simply not work!

 

We can only support up to 23 cascaded switches because message age increases with the maximum age timer on RSTP. The maximum STP diameter our switches can support is 23 (max-age =23).

 

It is strongly recommended to use aggregation switches with this given size of the network. You should also implement and consider as balaji said the hierarchical network design with the Access/Distribution and Core layers as a best practice. 

 

Sx350/550 could perfectly work as an aggregate or access switch whereas Sx250 is a good fit for an access switch.

 

Thanks

Martin

 

 

 

 

Thanks Martin,

 

what switches would you recommend?

Would stacking switches help?

 

Hello hallio,

 

Since stacking will reduce the total number of connected switches it will help. Default STP timer values are based on some assumptions about the size of the network and the length of the hello time. So those correspond to a network having a diameter of seven switches. It is also recommended if any changes need to be made like in your case (to expand the STP diameter/network diameter), only the network diameter value to be modified on the root bridge switch. When the diameter is changed, the switch calculated new values for all timers automatically.

 

With the Sx250/350/550 and CBS220/250/350 switches, you can't modify diameter parameters but only Hello Time, Max Age and Forward Delay parameters. I believe the maximum value of the diameter parameter in IOS-based Catalyst switches is 7 (for example https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swstp.html ), however, you can play with the other values and calculate the network diameter: https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/19120-122.html#calculate

 

The best approach would be to have a number of network segments with core or aggregation switches interconnected to each other.

 

Thanks,

Martin

 

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