IGMP Snooping Process Between the Source and a Second Receiver on the Same VLAN

Figure 9-5 illustrates what happens when a second host from the same VLAN sends a membership report to the router.

Figure 9-5. Host3 Sends a Membership Report

The following explains the process:

Step 1. Host3, on port 10/2, sends an unsolicited IGMP membership report to 239.1.1.1.

Step 2. The switch intercepts the IGMP message:

MCAST-IGMPQ:recvd an IGMP V2 Report on the port 10/2 vlanNo 3 GDA

  239.1.1.1

     In ModifyMulticastEarlEntry

The multicast forwarding table is updated with port 10/2:

Switch1 (enable) show multicast group 01-00-5e-01-01-01

VLAN  Dest MAC/Route Des   [CoS]  Destination Ports or VCs/[Protocol Type]

----  ------------------   -----  ---------------------------------------

3     01-00-5e-01-01-01              10/1-2,15/1

Step 3. The switch then sends the IGMP packet to the MSFC on port 15/1:

MCAST-RELAY:Relaying packet on port 15/1 vlanNo 3

MCAST-SEND: Inband Transmit Succeeded for IGMP RELAY msg on port 15/1 vlanNo 3

Step 4. The router receives the unsolicited IGMP Join from the receiver:

*Sep 30 06:07:41.434: IGMP: Received v2 Report on Vlan3 from 10.1.3.3

  for 239.1.

1.1

Step 5. MSFC updates its IGMP membership table:

msfc_15#show ip igmp group

IGMP Connected Group Membership

Group Address    Interface                Uptime    Expires   Last Reporter

239.1.1.1        Vlan3                       00:31:16  00:02:11  10.1.3.3

Step 6. Because the MSFC already has an outgoing interface (OIF) for VLAN 3, it will not do anything on the mroute table.

Step 7. No changes are made to the MMLS table. The MSFC does not send any shortcut information to the MMLS-Switching Engine (MMLS-SE) because Host3 is also part of VLAN 3:

msfc_15#show mls ip multicast group 239.1.1.1

Multicast hardware switched flows:

Total hardware switched flows : 0

Switch#1 (enable) show mls multicast entry

Router-IP       Dest-IP         Source-IP       Pkts                 Bytes

          InVlan Type OutVlans

--------------- --------------- --------------- -------------------- -----------

--------- ------ ---- -------------------------------------------

Total Entries Displayed: 0 (0 complete flow (C) and 0 partial flow (P))

IGMP Snooping Process Between the Source and a Second Receiver on the Same VLAN

IGMP Snooping Process Between the Source and a Second Receiver on the Same VLAN

Figure 9-5. Host3 Sends a Membership Report

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