Multicast traffic forwarding issue

[jonathan.lachaud1]

Hello,

In one of our electrical substation, we have a set of IEDs (substation equipments) connected to a CGS2520 (SWA-1 : fa0/2) and an other set o IEDs connected to another CGS2520 (SWA-1 : fa0/1). Both CGS are connected to each others using gigabit interface.

TCP connectionsbetween the two set of IED work just fine when the switchport is configured as an access port with the proper vlan membership(77). 

Anyway We are trying to send multicast traffic (goose message :https://en.wikipedia.org/wiki/Generic_Substation_Events) from the first set of IEDs to the second set of IED but it seems that switch does nor forward the multicast unless the port is configured as trunk with the proper vlan configured as native. We have tried to send the multicast traffic with Vlan header or without but in both case it does not work if the port are configured as an access port.

Switch is running 15.0(2)ED1.  We have performed some bug searches but have found nothing.

Do you have any idea about the source of the problem?

Thanks in advance.

[Philip D'Ath]

I have never used any of the bits of kit you mention, but let me apply some knowledge of multicast.

To "get" a multicast message the client has to subscribe to it.  Once the client subscribes to it then the switch will deliver that stream.

I'm guessing the trunk case is working because the switch is not sure so is forwarding the multicast group messages waiting on a prune to tell it to stop, which your end node will never send.

I found this guide about configuring multicast for that model.

http://www.cisco.com/c/en/us/td/docs/switches/connectedgrid/cgs2520/software/release/12_2_53_ex/configuration/guide/scg2520/swmcast.html

Configure the switch for "dense" mode.  This will cause it to presume everyone wants every multicast stream until it is pruned.  Presuming that your devices don't know how to do join messages they wont know how to do prune messages so this should cause multicast to go to every port no matter what.

Another method may be to use the "ip igmp static-group" command, and statically join the interfaces to the relevant multicast group.

Have an experiment and let us know which works easiest/best.

[Learner]

@ jonathan.lachaud1
Did u find a work around for this , i am using 4010 switch having the same issue.
This issuse is related to vlan priority tagging which goose message assigns before sending messages.
Although switch can recieve it but doesnt transmit the goose as it strips of vlan label.