topic Re: multicast routing between subnets in voss core and edge in ExtremeSwitching (VSP/Fabric Engine)

multicast routing between subnets in voss core and edge

louisbrinson — Thu, 16 Apr 2026 13:44:06 GMT

Hi Folks,

I have a RSMLT network with 2 VSP 8400's as the core. Edge network is Universal 5520's running VOSS. I have successfully managed to get ERS switches to route multicast traffic from one vlan to another and hit an endpoint on another set of ERS switches attached to the same core. I am having issue with that on the universal switches running VOSS though. Does anyone have a similar configuration out there or has found a document that outlines what igmp snoop settings are needed at each VOSS edge to make this work correctly?

I have SPB multicast enabled on each of the vlans that need multicast routing and have enabled multicast route discovery on them in the core as well. Again it works with our ERS edge switches just not with the VOSS edge switches. One of the requirements is that I do have to have a unicast IP on each of the endpoints as well as them being able to join a multicast group. I do not have the macsec\advanced license at the core which would allow me to make a L3VSN and enable multicast on it.

Any thoughts on this would be appreciated.

Re: multicast routing between subnets in voss core and edge

licamog561 — Fri, 17 Apr 2026 10:44:03 GMT

The problem seems to be with how the VOSS edge switches handle IGMP snooping. ERS doesn't require you to set up IGMP snooping querier on the VLANs where multicast receivers are located. Instead, VOSS does. You should also make sure that SPB multicast is always on across the fabric. Make sure that IGMP snooping is turned on for each VLAN on the Universal 5520s, that the querier is active if the core isn't providing one, and that multicast route discovery is linked to the right I-SIDs. If you don't have L3VSN multicast, you'll have to rely on the right snooping/querier setup at the edge to send traffic to the right place.

Re: multicast routing between subnets in voss core and edge

Roger_Lapuh — Fri, 17 Apr 2026 14:38:35 GMT

When running VOSS to the edge you will need to run MC-Lite. Multicast-lite will allow you to configure multicast to a VLAN/ISID. You can either turn on MC-lite through a VSA response or configure it through CLI by using the "mvpn" command and provide the L3 VSN context/ISID. If you want routed IP Multicast running IGMP snooping at the edge won't work. IGMP snooping is for the MC bridged only use case.

Re: multicast routing between subnets in voss core and edge

WillyHe — Sun, 19 Apr 2026 15:55:33 GMT

Hello,

This is how I remember me the MCAST-Lite configuration and how to use it in your setup..

You don’t specify that the core is in full SPBM configuration, to use “MCAST-Lite” one the edge it is required and have SPBM multicast generally enabled.
So that’s the first thing to do.

For the L2 MCAST vlan’s in the EDGE, L3 MUST be done on the core, but I assume this the case, and all L3 and IGMP configuration in the edge must be removed.
As for the CORE, SPBM multicast must be generally enabled on the EDGE switches.

MCAST-Lite configuration example

vlan create 10 name "MCAST-Lite_10" type port-mstprstp 0
interface Vlan 10
mvpn-isid 10 1
ip spb-multicast enable
ip igmp upnp-filter
ip igmp routed-spb-querier-addr 1.2.3.4
exit

vlan create 11 name "MCAST-Lite_11" type port-mstprstp 0
interface Vlan 11
mvpn-isid 10 1
ip spb-multicast enable
ip igmp upnp-filter
ip igmp routed-spb-querier-addr 1.2.3.4
exit

vlan create 20 name "MCAST-Lite_20" type port-mstprstp 0
interface Vlan 20
mvpn-isid 20 2
ip spb-multicast enable
ip igmp upnp-filter
ip igmp routed-spb-querier-addr 1.2.3.4
exit

vlan create 200 name "MCAST-Lite_200" type port-mstprstp 0
interface Vlan 200
mvpn-isid 20 3
ip spb-multicast enable
ip igmp upnp-filter
ip igmp routed-spb-querier-addr 1.2.3.4
exit

The “mvpn-isid” command allows to specify an I-SID id.
You can use different I-SID id’s for different VLAN’s.
Only vlan’s with the same “mvpn-isid” id. can exchange MCAST traffic, this allows to isolate some MCAST traffic to be exchanged between specific vlan’s.

The “ip igmp routed-spb-querier-addr” is optional, "0.0.0.0" is the default but some MCAST receivers have problems with that.

Check also the “IP Multicast config-lite” chapters in the “VOSS / Fabric Engine User Guides”.

Hope it helps
WillyHe

Re: multicast routing between subnets in voss core and edge

louisbrinson — Mon, 20 Apr 2026 11:47:03 GMT

Thank you for the replies folks, lots of very good information. In our environment it appears we may have to buy the MAC-SEC license. The vlans/i-sids need to be unicast IP routed as well as able to support multicast routing. The devices that will be in these networks are managed by unicast traffic and stream content via multicast.

My first attempt at this, the IGMP querier is at the core switch with the unicast IP and SPBM enabled on the vlan. Rather than just having the radius server assign the "AV" vlan/i-sid I created the AV VLAN on the edge switch and enabled snooping there. Obviously that didn't work and from your replies I see why.

Let me know if I'm thinking wrong about this but for me to be able to radius assign this MVPN network to a switch and it have a unicast IP address I'll have to buy the license for it. Is that correct?

Re: multicast routing between subnets in voss core and edge

louisbrinson — Mon, 20 Apr 2026 11:51:40 GMT

Hi Roger, What is the syntax for the VSA response? That is most likely how I'll need to do this on a large scale to support extron devices across all of our campuses. We do run our entire network on extreme control and don't do any port level config anymore so I'd build this in the appropriate core and then send it when a device authenticated and got the "AV" end system group.

Re: multicast routing between subnets in voss core and edge

louisbrinson — Wed, 22 Apr 2026 14:44:36 GMT

I managed to get a premier license on 2 of our cores that manage our campus network. I was not able to assign a unicast IP to the MVPN vlan though. I'm not really sure what mechanism will allow for us to use the Extron NAV encoders and manage them across multiple vlans.

We have to have a unicast IP to manage them from a central NAV server and a multicast network for the streams. Currently looking in to if the Extron devices will allow for tagged traffic so we can manage on one tagged i-sid and have the mvpn i-sid tagged as well. I'll post if/when I find a solution.

Re: multicast routing between subnets in voss core and edge

louisbrinson — Tue, 28 Apr 2026 16:50:21 GMT

Can you tell me where to configure multicast route discovery on an i-sid?