Configuring the Switching Fabric Bandwidth
By default, the switch fabric for the ERX-1440, ERX-310, E120, and E320 routers uses a bandwidth weighting ratio of 15:2 for multicast-to-unicast weighted round robin (WRR). In the absence of strict-priority traffic, and when both unicast and multicast traffic compete for switch fabric bandwidth, the switch fabric allocates 15/17ths of the available bandwidth to multicast traffic and 2/17ths of the available bandwidth to unicast traffic.
You can use the fabric weights command to change the ratio for multicast to unicast traffic on the router switch fabric. For more information about the fabric weights command, see JUNOSe System Basics Configuration Guide, Chapter 5, Managing the System.