Connect two switches with one cable per vlan

adamfon · ‎10-31-2021

I have two mobile server racks, each with a Cisco sg250. The switches have identical setups, with each port mapped to one of three vlans. The vlans are fully independent (I would have done three separate unmanaged switches instead if there was enough space in the rack)

Occasionally I have to connect these two racks together. I need to guarantee a full gigabit bandwidth for each of the vlan interconnects between the switches so ideally I would just use one interconnect cable per vlan, however STP is causing two of the three links to shut down.

Another option is to LAG three cables and trunk the vlans, but then there is no way to guarantee full gigabit bandwidth for each (e.g. if one vlan uses more than its gigabit bandwidth, it will affect the other two.)

Is there a better way to achieve this? (Other than putting 3 unmanaged switches in each rack.) Perhaps this is a job for Multiple STP?

marce1000 · ‎10-31-2021

>Another option is to LAG three cables and trunk the vlans, but then there is no way to guarantee full gigabit bandwidth for each (e.g. if one vlan uses more than its gigabit bandwidth, it will the other two.)

- The general view is to stick to these standard methodologies for transporting vlans, you will have the benefit of standard STP setups and algorithms. Usually bandwidth will not become an effective problem. If it should be then upgrading the switching environment with more powerful trunk links is better.

M.

-- Each morning when I wake up and look into the mirror I always say ' Why am I so brilliant ? '
When the mirror will then always repond to me with ' The only thing that exceeds your brilliance is your beauty! '

Georg Pauwen · ‎10-31-2021

Hello,

as far as I recall, the SG250 switches support PVST, so if you configure that, spanning tree should not get in the way...

paul driver · ‎10-31-2021

Hello

@adamfon wrote:

I need to guarantee a full gigabit bandwidth for each of the vlan

You could have 3 interfaces connecting the two switches via 3 access ports-
example:
interface GigabitEthernet0/1
switchport mode host

switchport access vlan 10
switchport mode access

interface GigabitEthernet0/2
switchport mode host
switchport access vlan 20
switchport mode access

interface GigabitEthernet0/3
switchport mode host
switchport access vlan 30
switchport mode access

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Kind Regards
Paul

adamfon · ‎10-31-2021

Would I not run into STP issues in this case?