A multicast group is assigned a multicast address (that is, an IP address in the 224.0.0.0/4 class D address space). Hosts registered to receive the stream join the group by sending an IGMP report to the upstream multicast router. The router then adds that group to the list of multicast groups that should be forwarded onto the local subnet.
The router does not maintain state about which hosts on the subnet are to receive traffic for the group. Instead, the router continues to send traffic to the subnet until either a timeout expires or there are no more hosts in that group on the subnet.
| Packets | Description |
|---|---|
| RD (8 Octets) | Route Distinguisher |
| Ethernet Segment Identifier (10 Octets) |
0 if (S,G) / (*,G) is learned on Cluster Edge Port (CEP) |
| Ethernet Tag ID (4 octets) |
0 or optionally set to the VLAN ID over which a multicast route is learned |
| Multicast Source Length (1 octet) |
32 for IPv4 address and 0 for wildcard address (*) |
| Multicast Source Address (variable) |
IP address of multicast source |
| Multicast Group Length (1 octet) |
32 for IPv4 address |
| Multicast Group Address (variable) |
IP address of multicast group |
| Originator Router Length (1 octet) |
32 for IPv4 address |
| Originator Router Address (variable) |
The IP address of the originating router |
| Flags (1 octets) (optional) |
The flag fields are defined in the Flags and values table. |
| Parameter | Value |
|---|---|
| Querier Config Sync | Multicast Group is set to 224.0.0.2. |
| Mrouter Sync | Multicast Group is set to 224.0.0.1. |
| Originator router length | IPv4 addresses: 32 |
| Originator router address | IP address of the originating router |
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Reserved | Querier config sync | Mrouter sync | PIM snooping | IE | V3 | V2 | V1 |
| Bit 1: QuerierConfigSync | Bit 2: MrouterSync | Bit 3: PIM snooping | Bit 4: (S, G) information carries the route-type of Include Group (bit value 0) or Exclude Group (bit value 1). The Exclude Group is ignored if bit 5 is set for IGMP v2, IGMP v1. | Bit 5: support for IGMP v3 | Bit 6: support for IGMP v2 | Bit 7: support IGMP v1 | |
| Bits 1, 2, and 3 are proprietary fields. | |||||||