The IP multicast technology enables a significant reduction in the amount of network traffic by delivering a single information stream to thousands and even larger numbers of consumers, which is especially efficient for voice and video traffic delivery. The traditional traffic delivery methods are unicast (point-to-point) and broadcast. Multicast allows delivery of traffic to a group of hosts, called a multicast group. The recipient hosts that want to receive this traffic must join (become members of) the corresponding multicast group. To add hosts to a multicast group, the Internet Group Management Protocol (IGMP) is used. A multicast group is identified by its multicast address. For multicast addresses, a Class D subnet is reserved with the most significant 4 bits set to 1110. Thus, the address range for multicasting is defined as 224.0.0.0-239.255.255.255.
Routers need to provide efficient traffic delivery from the multicast source to the recipients. For that purpose, the Protocol Independent Multicast (PIM) is used in routers.
Routers in a multicast environment can have one of the three roles: First Hop Router (FHR), Rendezvous Point (RP), and Last Hop Router (LHR). The FHR is located closest to the multicast source and is responsible for registering the source in the network. The RP is a catalog of available multicast sources for the Any Source Multicast (ASM) mode. The LHR is located closest to the multicast recipient. Clients (multicast recipients) in local networks connected to the LHR use the IGMP protocol to register in the multicast group of interest by sending an IGMP membership report message.
UserGate can be used as an LHR for the local networks connected to it. For client (recipient) registration, UserGate supports the IGMPv3 and IGMPv2 protocols.
For communicating with other multicast routers, UserGate can only use the PIM Sparse Mode (PIM-SM). This is a mode where multicast traffic is sent only to those recipients that have explicitly requested it. The recipients must periodically confirm their desire to receive multicast traffic.
UserGate supports the Source Specific Multicast (SSM) mode and Any Source Multicast (ASM) modes.
Source Specific Multicast (SSM) is used when the recipient of the traffic explicitly specifies a multicast source known to it. In this mode, addresses are written as follows:
rtp://<src_ip>@<group_address>:<port>
where src_ip is the multicast source address, group_address is the multicast group address, and port is the port. Example:
rtp://10.10.10.10@239.0.0.5:4344
In Any Source Multicast (ASM) mode, the multicast recipient specifies the multicast group from which it wants to receive multicast traffic. For this mode to work, a Rendezvous Point (RP) router is required. The RP determines the multicast source for this multicast group and this recipient, and then the source and recipient choose the best network path for sending this multicast traffic. In this mode, addresses are written as follows:
rtp://@<group_address>:<port>
where group_address is the multicast group address and port is the port. Example:
rtp://@239.0.0.5:4344
To configure UserGate as an LHR multicast router, follow these steps:
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Task |
Description |
|---|---|
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Step 1. Configure a multicast router. |
In the UserGate console, go to the Network --> Virtual routers section, select Multicast router in the menu, and configure it. |
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Step 2. Specify the interfaces on which this router will work. |
In the UserGate console, go to the Network --> Virtual routers section, select Interfaces in the menu, and configure the interfaces. Only the interfaces belonging to this virtual router are available for selection. |
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Step 3. (Optional) Define the Rendezvous points for ASM. |
In the UserGate console, go to the Network --> Virtual routers section, select Rendezvous points in the menu, and specify the addresses of the rendezvous points. |
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Step 4. (Optional) Set the desired restrictions on the available multicast groups for ASM. |
In the UserGate console, go to the Network --> Virtual routers section, select Rendezvous points in the menu, go to the ASM allowed groups tab, and specify the addresses of the allowed multicast groups. If you leave the list empty, all multicast group addresses will be allowed. |
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Step 5. (Optional) Set the desired restrictions on the available multicast groups for SSM. |
In the UserGate console, go to the Network --> Virtual routers section, select SSM allowed groups in the menu, and specify the addresses of the allowed multicast groups. If you leave the list empty, all multicast group addresses will be allowed. |
When configuring a multicast router, you can provide these settings:
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Name |
Description |
|---|---|
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Enabled |
Enables or disables the multicast router in this virtual router. |
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Use ECMP |
Enables multi-path traffic distribution using the Equal Cost Multi Path (ECMP) technology. Requires that several routes exist to the network node of interest. If this option is disabled, all traffic to a specific destination host will be sent through only one of the routers (next hop). |
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Use ECMP rebalance |
If this option is enabled and one of the interfaces used for sending traffic has gone offline, all existing streams will be redistributed between the remaining routes (next hop). If disabled, only those streams will be redistributed which were sent via the now-offline interface. |
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JOIN/PRUNE time (sec) |
The time interval in seconds (60-600) used to send messages to the PIM neighbors about multicast groups from which the router wants or no longer wants to receive traffic. |
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Multicast register suppress time (sec) |
The time interval in seconds (5-60,000) after which the router sends a register suppress message. |
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Keep-alive time (sec) |
The time interval in seconds (31-60,000) which the router will use to send keepalive messages to neighbors as well as the time to wait before considering the neighbor unavailable. |
When configuring interfaces, you can provide these settings:
|
Name |
Description |
|---|---|
|
Enabled |
Enables or disables multicasting on this interface. |
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Interface |
Select the interface that will be used for multicasting. Only the interfaces belonging to this virtual router are available for selection. |
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Multicast HELLO sending timeout (sec) |
The time interval in seconds (1-180) used to send PIM HELLO messages. These messages are sent periodically from all interfaces on which multicasting is enabled. These messages let the router know about neighbor routers that support multicasting. |
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DR selection priority |
The router's priority (1-4294967295) in the selection of a Designated router (DR). The administrator can use this to manage DR selection for the local network. |
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Enable IGMP |
Receive IGMP report and IGMP query messages on this interface. |
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Use IGMPv2 |
Use version 2 of IGMP. By default, version 3 (IGMP v3) is used. |
When configuring Rendezvous points, you can specify the following parameters:
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Name |
Description |
|---|---|
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Enabled |
Enables or disables this RP. |
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Name |
The RP name. |
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IP address |
The unicast IP address of this RP. |
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Allowed ASM groups |
The list of allowed multicast group addresses for any-source multicast from this RP. Any networks in the range 224.0.0.0/4. If empty, there are no restrictions. |
Allowed SSM groups: specifies the list of allowed multicast group addresses for source-specific multicast. Any networks from the range 232.0.0.0/8 can be specified. If empty, there are no restrictions.
SPT exclusions: specifies the list of IPv4 multicast groups excluded from switching to the shortest path tree.