The following instruction are valid for Cisco SG/CBS series and make the strong assumption that the user wants to avoid to use trunk ports but has pre-existing cabling that allows the switch interconnection to be based off physical network separation.
Here’s a diagram that represents such scenario:
The following instruction should allow the principle to be extended to even more VLANs and to be applied to newer generations Cisco switches.
Note : such configuration requires some network skills.
VLAN Management:
Create 2 VLANs (internet/office and RAVENNA)
Set all the ports in access mode
Select VLAN 1, and set Untagged as Membership type for all the ports to be assigned to VLAN 1. Exclude the ports to be assigned to VLAN 2. Repeat the process for VLAN 2 (the configurations will have to be mutually exclusive)
Port VLAN Membership will have to show something like this (1U = VLAN1 untagged, 2U =VLAN2 untagged). Double check the Port <--> VLAN mapping. U=untagged means that the packets leaving/entering the port are untagged, then the switch internally tags them)
Spanning tree:
To be sure STP will not block the interconnecting ports, we need to enable Multiple STP.
Fist we define a common region and revision (has to be the same for both the switches:
Then we need to map our VLANs to STP instances, in this example we map 1-1 and 2-2:
The last step will be to define STP “Path cost” for the ports we use to bridge the switches, per VLAN, which in this case correspond to MSTP instance. The idea is to make artificially very convenient to use a given port on a STP instance and another port on another instance (each instance being mapped to a different VLAN), by tweaking “Path Cost” for each switch port. So, we select Instance 1 on the top, we identify the port of VLAN1 interconnection, and we set the path cost to a considerably low value (e.g. 10). In this example, the designated port is 9:
In the same way, we select instance “2”, and we modify the path cost for VLAN 2 interconnect port. In this example it is port 10:
Once done, for instance 1, the corresponding port status must be “Forwarding” and while the other port needs to be in “Discarding” or “Listening status. See port 9 and 10 in the following picture:
Expect the same, but with inverted ports, on instance 2
One of the two switches will be elected as “root”. To control this, one can chance the priority field in STP global settings (lower value = higher priority):
Such root switch may show Forwarding/Listening on the ports as state. It’s expected (see port 9 and 10)
Multicast:
We finally have to make sure our multicast access is granted across the switches, propagating IGMP requests to be able to discover devices, streams and effectively transmit/receive audio.
First we need to enable IP group address for both our VLANs. Select VLAN ID, set to IP group, click apply. Repeat the steps for VLAN 2
Then, in IPv4 Multicast configuration → IGMP Snooping, enable snooping and IGMP querier:
Then, select each VLAN, click edit and make sure the settings for both VLAN match the following
The switch will take care of automatically forwarding IGMP requests for you and automatically elect an IGMP querier.