Configuring multicast VLANs 1

Overview·· 1

Multicast VLAN configuration task list 2

Configuring a multicast VLAN·· 2

Configuration guidelines 2

Configuration procedure· 3

Configuring the maximum number of forwarding entries in a multicast VLAN·· 3

Displaying and maintaining a multicast VLAN·· 3

Multicast VLAN configuration example· 4

 

Overview

In this chapter, the switch functions as a Layer 2 device (referred to as the switch in network diagrams); configurations for a Layer 3 device (referred to as the router in network diagrams) are implemented on an H3C router.

In the traditional multicast programs-on-demand mode shown in Figure 1, when hosts (Host A, Host B, and Host C) that belong to different VLANs require multicast programs-on-demand service, the Layer 3 device (Router A) must forward a separate copy of the multicast traffic in each user VLAN to the Layer 2 device (Switch A). In this case, a large amount of network bandwidth is used and an extra burden is added to the Layer 3 device.

Figure 1 Multicast transmission without the multicast VLAN feature

 

The multicast VLAN feature configured on the Layer 2 device is the solution to this issue. With the multicast VLAN feature, the Layer 3 device replicates the multicast traffic only in the multicast VLAN instead of making a separate copy of the multicast traffic in each user VLAN. This saves network bandwidth and lessens the burden on the Layer 3 device.

The multicast VLAN feature can be implemented in a sub-VLAN-based multicast VLAN.

As shown in Figure 2, Host A, Host B, and Host C are in three different user VLANs. On Switch A, configure VLAN 10 as a multicast VLAN, configure all user VLANs as sub-VLANs of this multicast VLAN, and enable IGMP snooping in the multicast VLAN.

Figure 2 A sub-VLAN-based multicast VLAN

 

After the configuration, IGMP snooping manages router ports in the multicast VLAN and member ports in the sub-VLANs. When forwarding multicast data to Switch A, Router A needs to send only one copy of multicast traffic to Switch A in the multicast VLAN, and Switch A distributes the traffic to the multicast VLAN's sub-VLANs that contain receivers.

For more information about IGMP snooping, router ports, and member ports, see "Configuring IGMP snooping." For more information about VLAN tags, see Layer 2—LAN Switching Configuration Guide.

Multicast VLAN configuration task list

Task	Remarks
Configuring a multicast VLAN	Required.
Configuring the maximum number of forwarding entries in a multicast VLAN	Optional.

 

Configuring a multicast VLAN

Before you configure a sub-VLAN-based multicast VLAN, complete the following tasks:

·     Create VLANs as required.

·     Enable IGMP snooping in the VLAN to be configured as a multicast VLAN.

By using this method, you need to configure a VLAN as a multicast VLAN, and then configure user VLANs as sub-VLANs of the multicast VLAN.

Configuration guidelines

·     You cannot configure a multicast VLAN on a device with IP multicast routing enabled.

·     The VLAN to be configured as a multicast VLAN must exist.

·     The VLANs to be configured as sub-VLANs must exist and must not be multicast VLANs or sub-VLANs of any other multicast VLAN.

·     The total number of sub-VLANs of a multicast VLAN must not exceed 1024.

Configuration procedure

To configure a sub-VLAN-based multicast VLAN:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Configure the specified VLAN as a multicast VLAN and enter multicast VLAN view.	multicast-vlan vlan-id	By default, a VLAN is not a multicast VLAN.
3.     Assign the specified VLANs to the multicast VLAN.	subvlan vlan-list	By default, a multicast VLAN has no sub-VLANs.

 

Configuring the maximum number of forwarding entries in a multicast VLAN

You can configure the maximum number of entries in the IGMP snooping forwarding table of a multicast VLAN. When the number of forwarding entries maintained for a multicast VLAN reaches the threshold, the system informs you to remove excessive entries. In this case, the system does not automatically remove any existing entries or create new entries.

To configure the maximum number of entries in the forwarding table:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Configure the maximum number of forwarding entries in a multicast VLAN.	multicast-vlan entry-limit limit	The default upper limit depends on the system operating mode. For more information, see Fundamentals Configuration Guide.

 

Displaying and maintaining a multicast VLAN

Task	Command	Remarks
Display information about a multicast VLAN.	display multicast-vlan [ vlan-id ] [ | { begin | exclude | include } regular-expression ]	Available in any view.

 

Multicast VLAN configuration example

IMPORTANT: By default, Ethernet interfaces, VLAN interfaces, and aggregate interfaces are in the state of DOWN. To configure such an interface, use the undo shutdown commands to bring it up first.

 

Network requirements

As shown in Figure 3, IGMPv2 runs on Router A, and IGMPv2 snooping runs on Switch A, Switch B, and Switch C. Router A acts as the IGMP querier.

The multicast source sends multicast data to multicast group 224.1.1.1. Host A, Host B, Host C, and Host D are receivers of the multicast group. The hosts belong to VLAN 2 through VLAN 5.

Configure the sub-VLAN-based multicast VLAN feature on Switch A so that Router A just sends multicast data to Switch A through the multicast VLAN and Switch A forwards the traffic to the receivers that belong to different user VLANs.

Figure 3 Network diagram

 

Configuration procedure

1.     Configure an IP address and subnet mask for each interface as per Figure 3. (Details not shown.)

2.     On Router A, enable IP multicast routing, enable PIM-DM on each Layer 3 interface, and enable IGMP on the host-side interface GigabitEthernet 3/0/2.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 3/0/1

[RouterA-GigabitEthernet3/0/1]port link-mode route

[RouterA-GigabitEthernet3/0/1] pim dm

[RouterA-GigabitEthernet3/0/1] quit

[RouterA] interface GigabitEthernet 3/0/2

[RouterA-GigabitEthernet3/0/2]port link-mode route

[RouterA-GigabitEthernet3/0/2] pim dm

[RouterA-GigabitEthernet3/0/2] igmp enable

3.     Configure Switch A:

# Enable IGMP snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

# Create VLAN 2 through VLAN 5.

[SwitchA] vlan 2 to 5

# Configure GigabitEthernet 3/0/2 as a trunk port, and assign it to VLAN 2 and VLAN 3.

[SwitchA] interface GigabitEthernet 3/0/2

[SwitchA-GigabitEthernet3/0/2] port link-type trunk

[SwitchA-GigabitEthernet3/0/2] port trunk permit vlan 2 3

[SwitchA-GigabitEthernet3/0/2] quit

# Configure GigabitEthernet 3/0/3 as a trunk port, and assign it to VLAN 4 and VLAN 5.

[SwitchA] interface GigabitEthernet 3/0/3

[SwitchA-GigabitEthernet3/0/3] port link-type trunk

[SwitchA-GigabitEthernet3/0/3] port trunk permit vlan 4 5

[SwitchA-GigabitEthernet3/0/3] quit

# Create VLAN 10, assign GigabitEthernet 3/0/1 to this VLAN, and enable IGMP snooping in the VLAN.

[SwitchA] vlan 10

[SwitchA-vlan10] port GigabitEthernet 3/0/1

[SwitchA-vlan10] igmp-snooping enable

[SwitchA-vlan10] quit

# Configure VLAN 10 as a multicast VLAN and configure VLAN 2 through VLAN 5 as its sub-VLANs.

[SwitchA] multicast-vlan 10

[SwitchA-mvlan-10] subvlan 2 to 5

[SwitchA-mvlan-10] quit

4.     Configure Switch B:

# Enable IGMP snooping globally.

<SwitchB> system-view

[SwitchB] igmp-snooping

[SwitchB-igmp-snooping] quit

# Create VLAN 2, assign GigabitEthernet 3/0/2 to VLAN 2, and enable IGMP snooping in the VLAN.

[SwitchB] vlan 2

[SwitchB-vlan2] port GigabitEthernet 3/0/2

[SwitchB-vlan2] igmp-snooping enable

[SwitchB-vlan2] quit

# Create VLAN 3, assign GigabitEthernet 3/0/3 to VLAN 3, and enable IGMP snooping in the VLAN.

[SwitchB] vlan 3

[SwitchB-vlan3] port GigabitEthernet 3/0/3

[SwitchB-vlan3] igmp-snooping enable

[SwitchB-vlan3] quit

# Configure GigabitEthernet 3/0/1 as a trunk port, and assign it to VLAN 2 and VLAN 3.

[SwitchB] interface GigabitEthernet 3/0/1

[SwitchB-GigabitEthernet3/0/1] port link-type trunk

[SwitchB-GigabitEthernet3/0/1] port trunk permit vlan 2 3

5.     Configure Switch C in the same way as you configure Switch B. (Details not shown.)

Verifying the configuration

# Display information about the multicast VLAN.

[SwitchA] display multicast-vlan

 Total 1 multicast-vlan(s)

 

 Multicast vlan 10

   subvlan list:

    vlan 2-5

# View the IGMP snooping multicast group information on Switch A.

[SwitchA] display igmp-snooping group

  Total 5 IP Group(s).

  Total 5 IP Source(s).

  Total 5 MAC Group(s).

 

  Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

  Subvlan flags: R-Real VLAN, C-Copy VLAN

  Vlan(id):2.

    Total 1 IP Group(s).

    Total 1 IP Source(s).

    Total 1 MAC Group(s).

    Router port(s):total 0 port(s).

    IP group(s):the following ip group(s) match to one mac group.

      IP group address:224.1.1.1

        (0.0.0.0, 224.1.1.1):

          Host port(s):total 1 port(s).

            GE3/0/2                (D)

    MAC group(s):

      MAC group address:0100-5e01-0101

          Host port(s):total 1 port(s).

            GE3/0/2

 

  Vlan(id):3.

    Total 1 IP Group(s).

    Total 1 IP Source(s).

    Total 1 MAC Group(s).

    Router port(s):total 0 port(s).

    IP group(s):the following ip group(s) match to one mac group.

      IP group address:224.1.1.1

        (0.0.0.0, 224.1.1.1):

          Host port(s):total 1 port(s).

            GE3/0/2                (D)

    MAC group(s):

      MAC group address:0100-5e01-0101

          Host port(s):total 1 port(s).

            GE3/0/2

 

  Vlan(id):4.

    Total 1 IP Group(s).

    Total 1 IP Source(s).

    Total 1 MAC Group(s).

    Router port(s):total 0 port(s).

    IP group(s):the following ip group(s) match to one mac group.

      IP group address:224.1.1.1

        (0.0.0.0, 224.1.1.1):

          Host port(s):total 1 port(s).

            GE3/0/3                (D)

    MAC group(s):

      MAC group address:0100-5e01-0101

          Host port(s):total 1 port(s).

            GE3/0/3

 

  Vlan(id):5.

    Total 1 IP Group(s).

    Total 1 IP Source(s).

    Total 1 MAC Group(s).

    Router port(s):total 0 port(s).

    IP group(s):the following ip group(s) match to one mac group.

      IP group address:224.1.1.1

        (0.0.0.0, 224.1.1.1):

          Host port(s):total 1 port(s).

            GE3/0/3                (D)

    MAC group(s):

      MAC group address:0100-5e01-0101

          Host port(s):total 1 port(s).

            GE3/0/3

 

  Vlan(id):10.

    Total 1 IP Group(s).

    Total 1 IP Source(s).

    Total 1 MAC Group(s).

    Router port(s):total 1 port(s).

            GE3/0/1                (D)

    IP group(s):the following ip group(s) match to one mac group.

      IP group address:224.1.1.1

        (0.0.0.0, 224.1.1.1):

          Host port(s):total 0 port(s).

    MAC group(s):

      MAC group address:0100-5e01-0101

          Host port(s):total 0 port(s).

The output shows that IGMP snooping maintains the router port in the multicast VLAN (VLAN 10) and the member ports in the sub-VLANs (VLAN 2 through VLAN 5).