The primary objective of this article is to provide guidance in troubleshooting Multicast on Junos OS devices (EX, SRX, or MX) acting as a Layer 3 device.

For configuration information or if your device is an EX switch configured as Layer 2, refer to KB21990 - Resolution Guides and Articles - Junos OS - Troubleshoot Multicast [juniper.net] .

• Multicast is not working through Junos OS device (EX, SRX, or MX) configured as Layer 3 device

• Multicast Client is not receiving data from Multicast source, with Junos OS device (EX, SRX, or MX) in the path

Note: This article does not apply to the following:

• IGMP v3

• SSM (Source Specific Multicast)

• PIM Dense mode

NOTE: Please take in consideration that for the MX-series routers a special hardware is require over the source Designated Router (DR) and the RP to encapsulate and de-encapsulate PIM register messages. Please refer to KB13329 - Setting up an MX-Series node for use as a Rendezvous Point (RP) in a Protocol Independent Multicast (PIM) Sparse-Mode [juniper.net] network for more information.

Perform the following steps to troubleshoot a PIM Sparse mode Multicast issue with an Junos OS device (EX, SRX, or MX) implemented at Layer 3:

Note: For the flowchart version of these steps, click the flowchart icon:

Map out your Network Topology and identify the following: For an example with definitions, refer to KB21591 - Sample Multicast Network Topology with Junos OS devices [juniper.net] .

LHR	(Last-Hop Router)
RP	(Rendezvous Point)
FHR	(First-Hop Router)
Multicast Client	(Receiver)
Multicast Server	(Source)
Multicast Group	(the group address not working)

Note:  Completion of this step is required before continuing.

Confirm that Unicast traffic connectivity is working between the Multicast Client (Receiver) and Server (Source).

• Unicast traffic must be working before continuing to troubleshoot Multicast.
• One way is to test Unicast traffic is to ping from the Multicast client to the Multicast server. (Check if ping is permitted on the devices.)
• If the ping response fails between the Multicast client and server, then narrow down the issue to the immediate next hop connected device to test if Unicast routing is working.
• Similarly from the upstream neighboring devices, follow the above step along the path taken by each next hop device to reach the server.

Do you have Unicast connectivity working between the Multicast Client and Server?

• Yes - Jump to Step 4
• No - Continue to Step 3

Ping from the LHR to the Multicast server. Do you have Unicast connectivity working between the LHR and Multicast server?

• Yes - Continue to Step 4
• No - Troubleshoot environment for Unicast connectivity. Also try ping from LHR to FHR. Unicast traffic must be working before continuing to troubleshoot Multicast.

On the LHR, verify that the LHR has received the Multicast stream from the source address S, for the Multicast Group G:

To do this, run the command:  show multicast route group <group address>    
For more information on reviewing the output, refer to KB21590 - [Junos] Verify if the Multicast stream for a specific Multicast group has been received on the LHR [juniper.net] .

Do you see the Multicast route for the particular group with the correct source?

• No - Continue to Step 5
• Yes - Multicast routing from Multicast source is good.  PIM is working properly.  Since the Multicast route for the specific group exists, it concludes that the Multicast stream has reached the LHR.  If the stream has still not reached the client, then proceed with troubleshooting downstream (including any L2 switch involved, the Multicast client, and the LHR's downstream interface). If still an issue, jump to Step 11 .

On the LHR, perform a RP check. 

To do this, run the command:   show pim rps extensive <group address>
For more information on reviewing the output, refer to KB21588 - [Junos] Verify if the RP information is configured on the LHR (Last-Hop Router) [juniper.net] .

Do you see the RP for the specific Multicast group configured?  

• Yes - Continue to Step 6
• No - RP configuration on the device needs to be verified.  Refer to KB21588 - [Junos] Verify if the RP information is configured on the LHR (Last-Hop Router) [juniper.net] .

On the LHR, verify the state of the PIM join on the device. 

To do this, run the command:   show pim join extensive <group address>
For more information on reviewing the output, refer to KB21903 - [Junos] Verify the status of the PIM join [juniper.net]
.

For the Multicast group in question, what is the Source?  

• Source is *   [also referred to as (*,G)] - Continue to Step 7
• Source is an IP address   [also referred to as (S,G)]  -
  Clear the Multicast group join by running the command: clear pim join <group-address>  
  
  Then run the ' show pim join ' and ' show multicast route ' commands again. 
  If you see (S,G), and if the device has still not received the Multicast traffic (stream) from the Source address S, for the Multicast Group G, then jump to Step 11 .  
  If you see (*,G) only, continue to Step 7 . 
  If the group is not listed, then follow the directions under 'Group is not listed'.
• Group is not listed - Device did not receive the PIM join.
  Run the command  show igmp group <group-address> to check if the group is listed. For example output, refer to show igmp group .
  If IGMP is not enabled, then enable IGMP for the downstream interface.   (Note: Enabling PIM also enables IGMP on the L3 interface.) 
  If IGMP is enabled, then perform L2 troubleshooting (i.e verify and correct connectivity between the client and LHR). Refer to Steps 7 and 8 in KB21585 - Resolution Guide - EX - Troubleshoot Multicast issue with EX device configured as Layer 2 switch [juniper.net] .

[PIM join is (*,G) on LHR]  On the LHR, verify the upstream and downstream interfaces for the PIM join are correct.

Look at the output of show pim join extensive <group-address>  
For more information on reviewing the output, refer to KB21903 - [Junos] Verify the status of the PIM join [juniper.net] .

The 'Upstream interface' should be the interface towards the RP.
The 'Downstream neighbors' should list all the L3 interfaces towards the Multicast receivers requesting the traffic for the specific group (i.e. vlan.101, vlan.102).

Are the upstream and downstream interfaces for the PIM join correct?        

• Yes - Continue to Step 8
• No -    If the 'Upstream interface' is blank, then this device is not seeing the RP, then jump to Step 11 .
  If the 'Downstream neighbors' are not all listed, the PIM join has not reached this device.  Check whether the PIM is configured properly between this device and the concerned downstream neighbor. 

  Move to the next PIM neighbor towards the RP, and verify the state of the PIM join on that device. 

To do this, run the command:  show pim join extensive <group-address>

For the Multicast group in question, what is the Source?

• Source is *   [also referred to as (*,G)] - Continue to Step 9
• Source is an IP address   [also referred to as (S,G)]
  Clear the Multicast group join by running the command:    clear pim join <group-address>  
  
  Then run the ' show pim join ' and ' show multicast route ' commands again. 
  If you see (S,G), and if the device has still not received the Multicast traffic (stream) from the Source address S, for the Multicast Group G, then jump to Step 11 .
  If you see (*,G) only, continue to Step 9 .
  If the group is not listed, then follow the directions for 'Group is not listed'.
• Group is not listed - Jump to Step 11

  [On this same PIM device] Are the upstream and downstream interfaces correct in the output of show pim join extensive group <group address> ?

The 'Upstream interface' should be the interface towards the RP.
The 'Downstream neighbors' should list all the L3 interfaces towards the Multicast receivers requesting the traffic for the specific group (i.e. vlan.101, vlan.102).

• Yes - Continue to Step 10
• No -    If the 'Upstream interface' is blank, then this device is not seeing the RP, jump to Step 11
  If the 'Downstream neighbors' are not all listed, the PIM join has not reached this device.  Check whether PIM is configured properly between this device and the concerned neighbor.  
  If all the Downstream neighbors are listed, then jump to Step 11 .

  Is the device that you performed 'steps 8 and 9' the RP? 

• No - Move to the next-hop router in the path to the RP, and go to Step 8         
  (Steps 8 and 9 will be repeated until you get to the RP.)
• Yes - On the RP, using a Firewall Filter, check if the Multicast source is sending the stream for that group.  If the RP is not receiving the stream, then perform the check on the FHR and other routers in the path to the Multicast source.  For Firewall Filter examples, refer to KB28405 - Firewall Filter Examples to verify Multicast traffic is reaching the Layer 3 Junos OS device [juniper.net] or KB21589 - Firewall Filter Examples to verify Multicast traffic is reaching the EX switch [juniper.net] .  Continue to Step 11, if still unresolved.

  Is the TTL in the Multicast stream sufficient to go from the Multicast source to the receiver?

• It is very common for a packet generator to default to TTL = 1 in Multicast streams used for testing. In this case, hosts in the same VLAN as the source will receive the Multicast, but no other hosts will.
• Check the source of the Multicast and verify that the TTL is higher than the number of Layer 3 hops from Source to Receiver. If this is not the issue, continue to Step 12 .

  If your problem is still not resolved, then collect the following and open a case with your technical support representative:

• Network diagram (with components labeled)

• Command output on all devices:

request support information
show route
show pim neighbors detail
show pim interfaces
show pim source detail
show pim join extensive
show multicast route extensive

• Additional Command output on the LHR:

show igmp group detail
show igmp interface detail
show igmp statistics interface ge-x/x/x

2020-04-30: Updated inactive links and also incorrect commands; verified all other links; article relevant and valid