Multicasting questions

Question

Ok,

Basic question is this.
show ip igmp snooping groups

Is not returning the multicast groups I am creating

More in-depth explanation.

I want to test multicast. I am on a flat network, and I just want to be able to multicast between clients on the same vlan, and even the same switch. I can use a multicast tool to mimic both a sending and receiving host. This tool works as expected on network A(where I know multicast works), while on network B I get a couple different results.

If multicasting between 2 hosts on the same Vlan and the same switch: Then I can transmit and receive, however, show ip igmp snooping groups is does not populate with the multicast group I am using.

Now I am not routing between vlans, and I am on the same switch /vlan.

here is the IGMP vlan config

show ip igmp snooping vlan 888
Global IGMP Snooping configuration:
-------------------------------------------
IGMP snooping              : Enabled
IGMPv3 snooping (minimal)  : Enabled
Report suppression         : Enabled
TCN solicit query          : Disabled
TCN flood query count      : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval : 1000

Vlan 888:
--------
IGMP snooping                       : Enabled
CAPWAP enabled                      : Disabled
IGMPv2 immediate leave              : Disabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000

My test multicast does seem to be transmitting/receiving correctly

Sending

Singlewire Software Packet 254  239.0.1.2:20480  TTL: 16
Singlewire Software Packet 255  239.0.1.2:20480  TTL: 16
Singlewire Software Packet 256  239.0.1.2:20480  TTL: 16
Singlewire Software Packet 257  239.0.1.2:20480  TTL: 16
Singlewire Software Packet 258  239.0.1.2:20480  TTL: 16
Singlewire Software Packet 259  239.0.1.2:20480  TTL: 16

Receiving

Receive Singlewire Software Packet 254 : 239.0.1.2:20480 : Receive Total 26
Receive Singlewire Software Packet 255 : 239.0.1.2:20480 : Receive Total 27
Receive Singlewire Software Packet 256 : 239.0.1.2:20480 : Receive Total 28
Receive Singlewire Software Packet 257 : 239.0.1.2:20480 : Receive Total 29
Receive Singlewire Software Packet 258 : 239.0.1.2:20480 : Receive Total 30
Receive Singlewire Software Packet 259 : 239.0.1.2:20480 : Receive Total 31

show ip igmp snooping groups

Seems to return these two unrelated multicast groups which are on a different vlan.

Switch#show ip igmp snooping groups
Vlan      Group                    Type        Version     Port List
-----------------------------------------------------------------------
889       224.0.5.128              igmp        v2          Fa0/33, Gi0/2
889       239.255.255.250          igmp        v2          Fa0/13, Gi0/2

Do I have to setup PIM/RP/etc on a layer 3 switch/router? How do you get a ip igmp snooping groups to populate on a layer 2 switch?

Answer 1

for the vlan you need to enable the multicast on it , it must configured to be interface vlan and under this interface configure * ip pim sparse-dense-mode*

something like
interface Vlan1
ip address 1.1.1.1 255.255.255.0
ip pim sparse-dense-mode
end

i found a very useful documentation that is talking about your problem exactly in this link Multicast Does Not Work in the Same VLAN in Catalyst Switches

Answer 2

If you want multicast to cross between different networks, all the routers in between the two networks must be multicast enabled. This is why you don't multicast on the Internet.

IGMP snooping will populate on a capable switch that has one or more hosts join IGMP on the router. IGMP snooping snoops on the IGMP conversation between the host and the router.