This article explains about the usage of SCB4 in the SRX5k chassis.
The SCB4 is supported on SRX5600 and SRX5800 Firewalls, but not supported on SRX5400 Firewalls.
The default fabric mode for SCB4 is Increased Fabric Bandwidth mode. Increased Fabric Bandwidth mode is the default fabric mode of SCB4. In this mode, it is required to install two SCB4s in SRX5600 and three SCB4s in SRX5800 Firewalls/Chassis clusters.
The fabric mode of SCB4 can be changed from Increased Fabric Bandwidth mode to Redundant Fabric mode using the CLI using command 'set chassis fabric redundancy-mode redundant'. If the fabric mode of SCB4 is changed to Redundant Fabric mode then it is required to install two SCB4s in SRX5600 and installation of either two or three SCB4s in SRX5800 Firewalls is required.
If the hardware is being upgraded from SCB3 (Redundant Fabric mode is the default fabric mode in SCB2 and SCB3) to SCB4 and installing only two SCB4s, then it is must to have Junos OS 19.3R1 or later and the change of default fabric mode of SCB4s to Redundant Fabric mode using the CLI is required.Note:- If the required number of SCB4s are not installed then the SRX will make CB Throughput Decreased alarm active on the SRX chassis. To mitigate the alarm, please refer "CB Fabric Throughput Decreased" on SRX5800 with SCB.