Devices performing different roles on a multicast network maintain different multicast tables, including the Internet Group Management Protocol (IGMP) group table, IGMP routing table, multicast protocol routing table, multicast routing table, and multicast forwarding information base (MFIB). The following sections describe the functions of these tables in multicast route management.
A multicast router creates an IGMP group entry when it receives an IGMP Join message from a host. The router maintains group memberships in IGMP group entries and instructs a multicast routing protocol, usually the Protocol Independent Multicast (PIM) protocol, to create corresponding (*, G) entries. The router maintains an IGMP group entry for each interface provided that the interfaces have IGMP enabled and have received IGMP Join messages.
The following is an example of a group entry on an interface:
<HUAWEI> display igmp group Interface group report information Vlanif100(10.1.6.2): Total 1 IGMP Group reported Group Address Last Reporter Uptime Expires 225.1.1.2 10.1.6.10 00:02:04 00:01:17
Table 1 explains the fields of this IGMP group entry.
| Field | Description |
|---|---|
| Group Address | Indicates the address of the group that an interface has joined. |
| Last Reporter | Indicates the IP address of the last user that sent an IGMP Join message to the group. |
| Uptime | Indicates the time elapsed since the group was created. |
| Expires | Indicates the time remaining before the group will be aged out. |
IGMP also maintains an IGMP routing table. An interface is included in an IGMP routing entry only when PIM is not enabled on the interface. The IGMP routing table increases the number of available outbound interfaces for multicast routing entries. The following is an example of an IGMP routing entry:
<HUAWEI> display igmp routing-table Routing table Total 1 entries 00001. (*, 225.1.1.1) List of 1 downstream interface Vlanif100 (10.20.20.1) Protocol: IGMP
Table 2 explains the fields in this IGMP routing entry.
| Field | Description |
|---|---|
| 00001. (*, 225.1.1.1) | 00001 is the entry number, and (*, 225.1.1.1) is an (*, G) entry, where * indicates any source and G indicates a group address. |
| List of 1 downstream interface | Indicates the downstream interfaces toward receivers. |
| Protocol: IGMP | Indicates the protocol that generates the downstream interfaces. |
According to the command output, the downstream interface is generated by IGMP, indicating that PIM is not enabled on the interface. If PIM is enabled on an interface, the routing entries of the interface are maintained by PIM.
Multicast routing protocols maintain their own routing tables to guide multicast route management. PIM is the most widely used multicast routing protocol. The following is an example of a PIM routing table:
<HUAWEI> display pim routing-table
VPN-Instance: public net
Total 0 (*, G) entry; 1 (S, G) entry
(192.168.0.12, 227.0.0.1)
RP: 10.2.2.2
Protocol: pim-sm, Flag: SPT LOC ACT
UpTime: 02:54:43
Upstream interface: Vlanif 10
Upstream neighbor: NULL
RPF prime neighbor: NULL
Downstream interface(s) information:
Total number of downstreams: 1
1: Vlanif 20
Protocol: pim-sm, UpTime: 02:54:43, Expires: 00:02:47
Table 3 explains the fields in this PIM routing entry.
| Field | Description |
|---|---|
| (192.168.0.12, 227.0.0.1) | (S, G) entry, where 192.168.0.12 is the source address and 227.0.0.1 is the group address. |
| RP: 10.2.2.2 | Indicates the rendezvous point (RP) IP address, which is displayed only when the protocol type is PIM-SM. |
| Protocol: pim-sm | The first Protocol field in an entry indicates the protocol that generates the entry, and the second Protocol field indicates the protocol that generates the downstream interfaces. |
| Flag: SPT LOC ACT | Indicates the flag of the PIM routing entry. |
| UpTime: 02:54:43 | The first UpTime field in an entry indicates how long the entry has existed, and the second UpTime field indicates how long a downstream interface has existed. |
| Upstream interface: Vlanif 10 | Indicates the upstream interface pointing to the multicast source. |
| Upstream neighbor: NULL | NULL indicates that no upstream neighbor is available. |
| RPF prime neighbor: NULL | NULL indicates that no reverse path check (RPF) neighbor is available. |
| Downstream interface(s) information: | Indicates information about downstream interfaces toward receivers. |
| Total number of downstreams: 1 | Indicates the number of downstream interfaces. |
| Expires: 00:02:47 | Indicates the aging time of a downstream interface. |
For details about PIM routing entries, see Concepts in the PIM feature description.
A multicast routing table is generated and maintained by the multicast route management module of a router. If a router supports multiple multicast protocols, its multicast routing table contains the optimal routes selected from the routing tables of these protocols.
In unicast routing, routing tables of various routing protocols, such as Open Shortest Path First (OSPF), Routing Information Protocol (RIP), and Border Gateway Protocol (BGP), constitute an IP routing table. Similarly, routing tables of different multicast protocols constitute a multicast table. Routers deliver multicast routing entries to their MFIBs to guide multicast data forwarding. The following is an example of a multicast routing table:
<HUAWEI> display multicast routing-table Multicast routing table Total 1 entry 00001. (192.168.0.2, 227.0.0.1) Uptime: 00:00:28 Upstream Interface: Vlanif10 List of 2 downstream interfaces 1: Vlanif20 2: Vlanif30
Table 4 explains the fields in this multicast routing entry.
| Field | Description |
|---|---|
| 00001. (192.168.0.2, 227.0.0.1) | 00001 is the entry number, and (FC00::2, FFE3::1) is an (S, G) entry, where S indicates a source address and G indicates a group address. |
| Uptime: 00:00:28 | Indicates the time elapsed since the multicast routing entry was updated. |
| Upstream Interface: VlanifIndicates the 10 | Indicates the upstream interface pointing to the multicast source. |
| List of 2 downstream interfaces | Indicates the downstream interfaces toward receivers. |
An MFIB is created and maintained by the route management module of a router according to multicast routing information. Routers forward multicast data according to their MFIBs. You can use the display multicast forwarding-table command to view entries in an MFIB. An MFIB has the same functions as a unicast FIB. The following is an example of an MFIB.
<HUAWEI> display multicast forwarding-table Multicast Forwarding Table Total 1 entry, 1 matched 00001. (10.10.10.2, 225.0.0.1) MID: 10, Flags: ACT Uptime: 00:08:32, Timeout in: 00:03:26 Incoming interface: Vlanif10 List of 1 outgoing interfaces: 1: Vlanif20 Activetime: 00:23:15 Matched 38264 packets(1071392 bytes), Wrong If 0 packets Forwarded 38264 packets(1071392 bytes)
Table 5 explains the fields in this multicast forwarding entry.
| Field | Description |
|---|---|
00001. (10.10.10.2, 225.0.0.1) |
00001 is the entry number, and (10.10.10.2, 225.0.0.1) is an (S, G) entry, where S indicates a source address and G indicates a group address. |
MID: 10 |
Indicates the unique identifier of the multicast forwarding entry in the MFIB. It is used to rapidly search the MFIB. |
Flags: ACT |
Indicates the flag of the multicast forwarding entry. |
| Uptime: 00:08:32 | Indicates how long the multicast forwarding entry has existed. |
| Timeout in: 00:03:26 | Indicates how soon the multicast forwarding entry will time out. |
| Incoming interface: Vlanif10 | Indicates the inbound interface in the multicast forwarding entry. |
| List of 1 outgoing interfaces: | Lists the outbound interfaces toward receivers. |
| Activetime: 00:23:15 | Indicates how long an outbound interface has existed. |
| Activetime: 00:23:15 | Indicates how long an outbound interface has existed. |
| Matched 38264 packets(1071392 bytes) | Indicates the number of packets that match the multicast forwarding entry. |
| Wrong If 0 packets | Indicates the number of packets that arrive on the incorrect inbound interfaces. |
| Forwarded 38264 packets(1071392 bytes) | Indicates the number of forwarded packets. |
The preceding information shows that multicast data is forwarded according to the MFIB. Each multicast forwarding entry records statistics about packets that are forwarded according to the entry.