looking for a couple of hints from you

we have a small but peculiar networking need: - 3 vlans, that are to be propagated among two L2 switches - we need to partition the vlans as much as possible, with the goal of

keeping latency as much as indipendent as possible

(one vlan traffic shouln't be able at all of "choking" the other ones, despite the heavy traffic)

we have two cisco sg 300 (28p) available, we had the idea of using

3 dedicated wires (one for each vlan) between the 2 switches

instead of using the usual "one-wire, trunk ports" layout.

we tried to implement it using both trunk and access mode ports, and dedicating a MST instance to house each vlan

but unfortunately, still, the switches seem to detect loops and one or more ports go (and stay) in Blocked status.

currently this is the situation

  • SwitchA_Port2 (access, VLAN2), connected through a dedicated wire to SwitchB_Port2 (access, VLAN2)
  • SwitchA_Port3 (access, VLAN3), connected through a dedicated wire to SwitchB_Port3 (access, VLAN3)
  • SwitchA_Port4 (access, VLAN4), connected through a dedicated wire to SwitchB_Port4 (access, VLAN4)

plus each switch has active the default VLAN1

  • MST1 <-> VLAN1
  • MST2 <-> VLAN2
  • MST3 <-> VLAN3
  • MST4 <-> VLAN4

on each switch, and the ids are matching.

unfortunately, i think that using a 3-wire link aggregation would not be the same, since it would "balance" the frames on the three wires, failing to achieve a real latency partitioning

can you suggest us what to look for to understand what we're doing wrong?

thanks a lot


Why not use a 3 cable LAG and configure QoS? That would give you redundancy, more potential throughput for your critical app, and make sure the critical app had priority?


Correct me if I'm wrong, but if you have vlan 1 active on all 3 ports, wouldn't spanning tree rightfully detect a loop and shut the port down?

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