Configuring the Switch 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.