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Sample Multicast Network Topology with Junos OS devices

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Article ID: KB21591 KB Last Updated: 28 Apr 2020Version: 3.0
Summary:

This article provides information about the Multicast topology and related terminologies to aid in troubleshooting Multicast issues.

Symptoms:

When troubleshooting Multicast issues, it is important to collect the network topology and label the key components.

Mapping out your network topology is required for the KB21990 - Resolution Guides - Troubleshoot Multicast.  It is also required if a technical support case need to be opened.

Solution:

Sample Network Topology:

Below is a sample network diagram with the primary components labeled in red.

  • LHR  (Last Hop Router)
  • RP (Rendezvous Point)
  • FHR  (First Hop Router)
  • Multicast Client (Receiver)
  • Mulitcast Server (Source)
  • Multicast Group

Identifying and understanding terminologies in the Multicast Topology

Below are brief definitions of the network topology components:

  • LHR (Last Hop Router):

    The LHR (where the receiver is connected) receives an IGMP join message; it then sends a PIM Join towards the RP. This creates a shared tree from the Last Hop Router to the RP along the routers. So, a shared tree is created from the Last Hop Router to the RP.

    The LHR sends the Group ID without the Multicast Group’s Source (*, G) to the next-hop Multicast Router, towards the (predefined) RP.

  • RP (Rendezvous Point):

    The RP router serves as the information exchange point for the other routers. All routers in a PIM domain must provide mapping to a RP router. It is the only router that needs to know the active sources for a domain.

    The other routers just need to know how to get to the RP. In this way, the RP matches receivers with sources. The RP router is downstream from the source and forms one end of the SPT (Shortest-Path Tree) and is the shortest path between the Multicast sender and the receiver.

    The RP router is upstream from the receiver and thus forms the other end of the RPT (Rendezvous Point tree).

     RP will receive both IGMP Register (S, G) and  IGMP Join (*, G).

  • FHR (First Hop Router):

    The FHR (where the source is connected) forwards the Group ID and its Multicast Group’s Source (S, G) to the next-hop Multicast Router, towards the (predefined) RP.  When the Multicast Server sends the Multicast stream, the First Hop Router encapsulates the Multicast packets into the PIM register messages and unicasts them to the RP as (S,G).

  • Multicast Client (Receiver):

    The Multicast receiver requests streams from the server by forwarding the IGMP join message to the LHR (Lost Hop Router).

  • Multicast Server (Source):

    The Multicast source sends the stream on a Multicast group address, for which the client has requested.

  • Multicast Group:

    The group address on which the server / source is streaming the Multicast traffic.
Technical Documentation References

For more information on Multicast, refer to the following links:

Multicast Protocols
Multicast Feature Guide for SRX Security Devics
 
Configurations

The configuration for the devices in the above sample network topology is:

Layer 2 - EX
set vlans CLIENT vlan-id 100
set vlans CLIENT interface ge-0/0/10.0
set vlans CLIENT interface ge-0/0/11.0
set interfaces ge-0/0/15 unit 0 family ethernet-switching port-mode trunk vlan members all


LHR
set vlans CLIENT vlan-id 100 l3-interface vlan.100
set interfaces ge-0/0/10 unit 0 family inet address 192.168.10.1/24
set interfaces ge-0/0/20 unit 0 family inet address 192.168.20.1/24
set interfaces vlan unit 100 family inet address 192.168.100.1/24
set interfaces ge-0/0/15 unit 0 family ethernet-switching port-mode trunk vlan members all
set protocols igmp interface vlan.100
set protocols ospf area 0.0.0.0 interface ge-0/0/10.0
set protocols ospf area 0.0.0.0 interface ge-0/0/20.0
set protocols ospf area 0.0.0.0 interface vlan.100
set protocols pim rp static address 192.168.1.1
set protocols pim interface ge-0/0/10.0
set protocols pim interface ge-0/0/20.0
set protocols pim interface vlan.100


If LHR is a SRX, see note for SRX devices at the end of this article for additional required configuration.

RP
set interfaces ge-0/0/20 unit 0 family inet address 192.168.20.2/24
set interfaces ge-0/0/15 unit 0 family inet address 192.168.15.1/24
set interfaces lo0 unit 0 family inet address 192.168.1.1/24
set protocols ospf area 0.0.0.0 interface ge-0/0/15.0
set protocols ospf area 0.0.0.0 interface ge-0/0/20.0
set protocols ospf area 0.0.0.0 interface lo0.0
set protocols pim rp local address 192.168.1.1
set protocols pim interface ge-0/0/20.0
set protocols pim interface ge-0/0/15.0


If RP is a SRX, see note for SRX devices at the end of this article for additional required configuration.

Other L3 EX
set interfaces ge-0/0/10 unit 0 family inet address 192.168.10.2/24
set interfaces ge-0/0/16 unit 0 family inet address 192.168.16.1/24
set interfaces lo0 unit 0 family inet address 192.168.1.2/24
set protocols ospf area 0.0.0.0 interface ge-0/0/15.0
set protocols ospf area 0.0.0.0 interface ge-0/0/20.0
set protocols ospf area 0.0.0.0 interface lo0.0
set protocols pim rp static address 192.168.1.1
set protocols pim interface ge-0/0/10.0
set protocols pim interface ge-0/0/16.0


FHR
set vlans SERVER vlan-id 200 l3-interface vlan.200
set interfaces vlan unit 200 family inet address 192.168.200.1/24
set vlans SERVER interface ge-0/0/10.0
set vlans SERVER interface ge-0/0/11.0
set interfaces ge-0/0/16 unit 0 family inet address 192.168.16.2/24
set interfaces ge-0/0/15 unit 0 family inet address 192.168.15.2/24
set protocols ospf area 0.0.0.0 interface ge-0/0/15.0
set protocols ospf area 0.0.0.0 interface ge-0/0/16.0
set protocols ospf area 0.0.0.0 interface vlan.200
set protocols pim rp static address 192.168.1.1
set protocols pim interface ge-0/0/15.0
set protocols pim interface ge-0/0/16.0
set protocols pim interface vlan.200


If FHR is a SRX, see note for SRX devices for additional required configuration.
 
Note for SRX devices:   If your LHR or FHR or RP is a SRX, then PIM must be enabled on the relevant security zones, and security policies must be created to allow the traffic between the security zones. See steps 3 and 4 in KB28362 - [SRX] Configuration example - Multicast PIM Sparse Mode for more information. 

For example, if the LHR in this topology is a SRX, it also needs this configuration:
set security zones security-zone trust address-book address 192.168.100.0 192.168.100.0/24
set security zones security-zone trust host-inbound-traffic protocols pim
set security zones security-zone trust interfaces ge-0/0/15.0
set security zones security-zone untrust address-book address 224.100.100.100 224.100.100.100/32
set security zones security-zone untrust host-inbound-traffic protocols pim
set security zones security-zone untrust interfaces ge-0/0/10.0
set security zones security-zone untrust interfaces ge-0/0/20.0
set security policies from-zone trust to-zone untrust policy p1 match source-address 192.168.100.0
set security policies from-zone trust to-zone untrust policy p1 match destination-address 224.100.100.100
set security policies from-zone trust to-zone untrust policy p1 match application junos-udp-any
set security policies from-zone trust to-zone untrust policy p1 then permit
Modification History:
2020-04-28: Fixed inactive links.
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