Multicast Source Only

Switch1 (enable) show igmp groupinfo 3 01-00-5e-01-01-01

MAC Address:              01-00-5e-01-01-01

Multicast Flag:           TRUE

confMask:                [0-4-0-0]

ltl_index:                0x500

mcast_info->protocol_type 2 = PROTO_TYPE_IGMP

mcast_info->protocol_type->info::

tx_v1_report:                FALSE

tx_v2_report:                TRUE

wait_count:               0

mcast_source_only:        FALSE

IP Address:               239.1.1.1

Host List::               15/1

Router Port  List::       10/1,15/1

User Conf Port List::     

V1 Host List::

report_rx_portlist::      15/1

The following steps outline the IGMP snooping process for the first host on VLAN 3 that sends a membership report for group 239.1.1.1:

Step 1. Host2 sends an unsolicited IGMP membership report to 239.1.1.1. The MSFC, port 15/1, is the router port for this traffic:

Switch1 (enable) show multicast router

Port       Vlan

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

15/1       3

Total Number of Entries = 3

'*' - Configured

'+' - RGMP-capable

Step 2. The switch that intercepted the IGMP message creates an EARL entry for Host2:

MCAST-IGMPQ:recvd an IGMP V2 Report on the port 10/1 vlanNo 3 GDA

  239.1.1.1

     In ModifyMulticastEarlEntry

     Creating new entry because it's the first Node

     Creating initial node in ModifyMulticast

     Updating portlist for initial hostlist add

The entry now is in the multicast forwarding table for the Group Destination Address (GDA), 239.1.1.1 (01-00-5e-01-01-01):

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           10/1,15/1

Multicast MAC addresses that appear in the forwarding table are stored as static entries in the CAM table. From the switch perspective, 239.1.1.1 is now associated with ports 10/1 and 15/1 on VLAN 3:

Switch1 (enable) show cam static 3

* = Static Entry. + = Permanent Entry. # = System Entry. R = Router Entry.

X = Port Security Entry $ = Dot1x Security Entry

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

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

3     01-00-5e-00-01-28           10/1,15/1

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

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, Host2 with an IP address of 10.1.3.2:

*Sep 30 05:58:47.830: IGMP: Received v2 Report on Vlan3 from 10.1.3.2

  for 239.1.



1.1

Step 5. The MSFC updates its IGMP membership table. The IGMP group membership provides information on the last host that requested the multicast traffic for that subnet:

msfc_15#show ip igmp group

IGMP Connected Group Membership

Group Address    Interface           Uptime    Expires   Last Reporter

239.1.1.1        Vlan3               00:21:54  00:02:39  10.1.3.2

Step 6. Next, the MSFC populates the mroute table, which is the equivalent of the IP route table for multicast. It will create the (*, g) and (S, G) entries for 239.1.1.1 and forward the traffic out on VLAN 3:

msfc_15#show ip mroute 239.1.1.1

IP Multicast Routing Table

Flags: D - Dense, S - Sparse, s - SSM Group, C - Connected, L - Local,

       P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set,

      J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running

      A - Advertised via MSDP, U - URD, I - Received Source Specific Host

           Report

Outgoing interface flags: H - Hardware switched

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.1.1.1), 00:06:25/00:02:59, RP 0.0.0.0, flags: DJC

  Incoming interface: Null, RPF nbr 0.0.0.0

  Outgoing interface list:

    Vlan3, Forward/Sparse-Dense, 00:06:25/00:00:00

(10.1.3.5, 239.1.1.1), 00:00:18/00:02:41, flags: PCT

  Incoming interface: Vlan3, RPF nbr 0.0.0.0

  Outgoing interface list: Null

Step 7. Multicast multilayer switching (MMLS) is enabled by default on Catalyst 6500 switches. In this case, because both source and destination are on the same VLAN, no hardware shortcut is created on the MSFC. This flow is already being handled by hardware switching. As a result, there will be no multicast MLS entry:

msfc_15#show mls ip multicast group 239.1.1.1

Multicast hardware switched flows:

Total hardware switched flows : 0

Switch1 (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))

Multicast Source Only

Multicast Source Only

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