Supported Platforms
Understanding Multicast Routing on a Chassis Cluster
Multicast routing support across nodes in a chassis cluster allows multicast protocols, such as Protocol Independent Multicast (PIM) versions 1 and 2, Internet Group Management Protocol (IGMP), Session Announcement Protocol (SAP), and Distance Vector Multicast Routing Protocol (DVMRP), to send traffic across interfaces in the cluster. Note, however, that the multicast protocols should not be enabled on the chassis management interface (fxp0) or on the fabric interfaces (fab0 and fab1). Multicast sessions will be synched across the cluster and will be maintained during redundant group failovers. During failover, as with other types of traffic, there might be some multicast packet loss.
Multicast data forwarding in a chassis cluster uses the incoming interface to determine whether or not the session remains active. Packets will be forwarded to the peer node if a leaf session’s outgoing interface is on the peer instead of on the incoming interface’s node. Multicast routing on a chassis cluster supports tunnels for both incoming and outgoing interfaces.
Multicast traffic has an upstream (toward source) and downstream (toward subscribers) direction in traffic flows. The devices replicate (fanout) a single multicast packet to multiple networks that contain subscribers. In the chassis cluster environment, multicast packet fanouts can be active on either nodes.
If the incoming interface is active on the current node and backup on the peer node, then the session is active on the current node and backup on the peer node.
Multicast configuration on a chassis cluster is the same as multicast configuration on a standalone device. See the Junos OS Routing Protocols Library for Security Devices for more information.
Understanding PIM Data Forwarding
Protocol Independent Multicast (PIM) is used between devices to track the multicast packets to be forwarded to each other.
A PIM session encapsulates multicast data into a PIM unicast packet. A PIM session creates the following sessions:
- Control session
- Data session
The data session saves the control session ID. The control session and the data session are closed independently. The incoming interface is used to determine whether the PIM session is active or not. If the outgoing interface is active on the peer node, packets are transferred to the peer node for transmission.
Understanding Multicast and PIM Session Synchronization
Synchronizing multicast and PIM sessions helps to prevent packet loss due to failover because the sessions do not need to be set up again when there is a failover.
In PIM sessions, the control session is synchronized to the backup node, and then the data session is synchronized.
In multicast sessions, the template session is synchronized to the peer node, then all the leaf sessions are synchronized, and finally the template session is synchronized again.
