Configuring PIM snooping································································································································································ 1

PIM snooping overview···························································································································································· 1

Configuring PIM snooping······················································································································································ 2

Displaying and maintaining PIM snooping························································································································ 2

PIM snooping configuration example·································································································································· 3

Troubleshooting PIM snooping··············································································································································· 6

PIM snooping does not work········································································································································· 6

Some downstream PIM-capable routers cannot receive multicast data···························································· 6

 

PIM snooping overview

Protocol Independent Multicast (PIM) snooping runs on Layer 2 devices. It determines which ports are interested in multicast data by analyzing the received PIM messages, and adds the ports to a multicast forwarding entry to make sure that multicast data can be forwarded to only the ports that are interested in the data.

Figure 1 Multicast packet transmission without or with PIM snooping

 

As shown in Figure 1, Source 1 sends multicast data to multicast group G1, and Source 2 sends multicast data to multicast group G2. Receiver 1 belongs to G1, and Receiver 2 belongs to G2. The Layer 2 switch’s interfaces that connect to the PIM-capable routers are in the same VLAN.

When running IGMP snooping without PIM snooping, the Layer 2 switch maintains the router ports according to PIM hello messages received from PIM-capable routers, broadcasts all other types of received PIM messages in the VLAN, and forwards all multicast data to all router ports in the VLAN. Each PIM-capable router in the VLAN, whether interested in the multicast data or not, will receive all multicast data and all PIM messages except for PIM hello messages.

When running both IGMP snooping and PIM snooping, the Layer 2 switch determines whether PIM-capable routers are interested in the multicast data addressed to a multicast group according to PIM messages received from the routers, and adds only the ports for connecting the routers that are interested in the data to a multicast forwarding entry. Then, the Layer 2 switch forwards PIM messages and multicast data to only the routers that are interested in the data, saving network bandwidth.

 

NOTE: ·       For more information about IGMP snooping and the router port, see the chapter “Configuring IGMP snooping.” ·       For more information about PIM, see the chapter “Configuring PIM.”

 

Configuring PIM snooping

Before configuring PIM snooping for a VLAN, be sure to enable IGMP snooping globally and specifically for the VLAN.

To configure PIM snooping:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enable IGMP snooping globally and enter IGMP snooping view.	igmp-snooping	Disabled by default
3.     Return to system view.	quit	N/A
4.     Enter VLAN view.	vlan vlan-id	N/A
5.     Enable IGMP snooping in the VLAN.	igmp-snooping enable	Disabled by default
6.     Enable PIM snooping in the VLAN.	pim-snooping enable	Disabled by default

 

NOTE: ·       For more information about the igmp-snooping and igmp-snooping enable commands, see IP Multicast Command Reference. ·       After you enable PIM snooping in a VLAN, PIM snooping works only on the member interfaces of the VLAN. ·       PIM snooping does not work in the sub-VLANs of a multicast VLAN. For more information about multicast VLAN, see the chapter “Configuring multicast VLANs.”

 

Displaying and maintaining PIM snooping

 

Task	Command	Remarks
Display PIM snooping neighbor information.	display pim-snooping neighbor [ vlan vlan-id ] [ slot slot-number ] [ | { begin | exclude | include } regular-expression ]	Available in any view
Display PIM snooping routing entries.	display pim-snooping routing-table [ vlan vlan-id ] [ slot slot-number ] [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the statistics of received PIM messages.	display pim-snooping statistics [ | { begin | exclude | include } regular-expression ]	Available in any view
Clear the statistics of received  PIM messages.	reset pim-snooping statistics	Available in user view

 

PIM snooping configuration example

Network requirements

As shown in Figure 2, Source 1 sends multicast data to multicast group 224.1.1.1, and Source 2 sends multicast data to multicast group 225.1.1.1. Receiver 1 belongs to multicast group 224.1.1.1, and Receiver 2 belongs to multicast group 225.1.1.1. Router C and Router D run IGMP on their interface GigabitEthernet 3/1/1. Router A, Router B, Router C, and Router D run PIM-SM, and interface GigabitEthernet 3/1/2 on Router A acts as a C-BSR and C-RP.

Configure IGMP snooping and PIM snooping on Router E so that Router E forwards PIM messages and multicast data to only the routers that are interested in the multicast data.

Figure 2 Network diagram

 

Configuration procedure

1.      Assign IP addresses:

Configure an IP address and subnet mask for each interface according to Figure 2. (Details not shown)

2.      Configure Router A:

# Enable IP multicast routing, enable PIM-SM on each interface, and configure interface GigabitEthernet 3/1/2 as a C-BSR and C-RP.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 3/1/1

[RouterA-GigabitEthernet3/1/1] pim sm

[RouterA-GigabitEthernet3/1/1] quit

[RouterA] interface GigabitEthernet 3/1/2

[RouterA-GigabitEthernet3/1/2] pim sm

[RouterA-GigabitEthernet3/1/2] quit

[RouterA] pim

[RouterA-pim] c-bsr GigabitEthernet 3/1/2

[RouterA-pim] c-rp GigabitEthernet 3/1/2

3.      Configure Router B:

 # Enable IP multicast routing, and enable PIM-SM on each interface.

<RouterB> system-view

[RouterB] multicast routing-enable

[RouterB] interface GigabitEthernet 3/1/1

[RouterB-GigabitEthernet3/1/1] pim sm

[RouterB-GigabitEthernet3/1/1] quit

[RouterB] interface GigabitEthernet 3/1/2

[RouterB-GigabitEthernet3/1/2] pim sm

4.      Configure Router C:

# Enable IP multicast routing, enable PIM-SM on each interface, and enable IGMP on GigabitEthernet 3/1/1.

<RouterC> system-view

[RouterC] multicast routing-enable

[RouterC] interface GigabitEthernet 3/1/1

[RouterC-GigabitEthernet3/1/1] pim sm

[RouterC-GigabitEthernet3/1/1] igmp enable

[RouterC-GigabitEthernet3/1/1] quit

[RouterC] interface GigabitEthernet 3/1/2

[RouterC-GigabitEthernet3/1/2] pim sm

5.      Configure Router D:

The configuration on Router D is similar to that on Router C. (Details not shown)

6.      Configure Router E:

# Enable IGMP snooping globally.

<RouterE> system-view

[RouterE] igmp-snooping

[RouterE-igmp-snooping] quit

# Switch the link mode of GigabitEthernet 3/1/1 through GigabitEthernet 3/1/4 to Layer 2 mode, create VLAN 100, assign GigabitEthernet 3/1/1 through GigabitEthernet 3/1/4 to this VLAN, and enable IGMP snooping and PIM snooping in the VLAN.

[RouterE] interface GigabitEthernet 3/1/1

[RouterE-GigabitEthernet3/1/1] port link-mode bridge

[RouterE-GigabitEthernet3/1/1] quit

[RouterE] interface GigabitEthernet 3/1/2

[RouterE-GigabitEthernet3/1/2] port link-mode bridge

[RouterE-GigabitEthernet3/1/2] quit

[RouterE] interface GigabitEthernet 3/1/3

[RouterE-GigabitEthernet3/1/3] port link-mode bridge

[RouterE-GigabitEthernet3/1/3] quit

[RouterE] interface GigabitEthernet 3/1/4

[RouterE-GigabitEthernet3/1/4] port link-mode bridge

[RouterE-GigabitEthernet3/1/4] quit

[RouterE] vlan 100

[RouterE-vlan100] port GigabitEthernet 3/1/1 to GigabitEthernet 3/1/4

[RouterE-vlan100] igmp-snooping enable

[RouterE-vlan100] pim-snooping enable

[RouterE-vlan100] quit

7.      Verify the configuration:

# On Router E, display  PIM snooping neighbor information about VLAN 100.

[RouterE] display pim-snooping neighbor vlan 100

  Total number of neighbors: 4

 

  VLAN ID: 100

    Total number of neighbors: 4

    Neighbor        Port                     Expires   Option Flags

    10.1.1.1        GE3/1/1                   02:02:23  LAN Prune Delay

    10.1.1.2        GE3/1/2                   03:00:05  LAN Prune Delay

    10.1.1.3        GE3/1/3                   02:22:13  LAN Prune Delay

    10.1.1.4        GE3/1/4                   03:07:22  LAN Prune Delay

The output shows that Router A, Router B, Router C, and Router D are PIM snooping neighbors.

# On Router E, display PIM snooping routing information about VLAN 100.

[RouterE] display pim-snooping routing-table vlan 100

  Total 2 entry(ies)

  FSM Flag: NI-no info, J-join, PP-prune pending

 

  VLAN ID: 100

    Total 2 entry(ies)

    (*, 224.1.1.1)

      Upstream neighbor: 10.1.1.1

        Total number of downstream ports: 1

          1: GE3/1/3

    (*, 225.1.1.1)

      Upstream neighbor: 10.1.1.1

        Total number of downstream ports: 1

          1: GE3/1/4

The output shows that Router E will forward the multicast data intended for multicast group 224.1.1.1 to only Router C, and forward the multicast data intended for multicast group 225.1.1.1 to only Router D.

Troubleshooting PIM snooping

PIM snooping does not work

Symptom

PIM snooping does not work on the router.

Analysis

IGMP snooping or PIM snooping is not enabled on the router.

Solution

1.      Use the display current-configuration command to check the status of IGMP snooping and PIM snooping.

2.      If IGMP snooping is not enabled, enter system view and use the igmp-snooping command to enable IGMP snooping globally. Then, enter VLAN view and use the igmp-snooping enable and pim-snooping enable commands to enable IGMP snooping and PIM snooping in the VLAN.

3.      If PIM snooping is not enabled, enter VLAN view and use the pim-snooping enable command to enable PIM snooping in the VLAN.

Some downstream PIM-capable routers cannot receive multicast data

Symptom

In a network with fragmented join/prune messages, some downstream PIM-capable routers cannot receive multicast data.

Analysis

PIM snooping cannot reassemble messages, and it cannot maintain the status of downstream routers that the join/prune message fragments carry. To ensure the normal operation of the system, PIM snooping must broadcast join/prune message fragments in the VLAN. However, if the VLAN has a PIM-capable router that has the join suppression function enabled, the broadcast join/prune message fragments might suppress the join messages of other PIM-capable routers in the VLAN. As a result, some PIM-capable routers cannot receive the multicast data addressed to a specific multicast group because their join messages are suppressed. To solve this problem, disable the join suppression function on all PIM-capable routers that connect to the PIM snooping-capable router in the VLAN.

Solution

1.      Use the pim hello-option neighbor-tracking command to enable the neighbor tracking function on the interfaces of PIM routers that connect to the PIM snooping-capable router.

2.      If a PIM-capable router cannot be enabled with the neighbor tracking function, you have to disable PIM snooping on the PIM snooping-capable router.