The correct answers are A and B. In SRX chassis clustering, the fabric link, represented by fab interfaces, is the data-plane connection between the two cluster nodes. Juniper describes the fabric as the back-to-back data connection used when traffic on one node must be processed on the other node or must exit through an interface on the other node; session-state information also passes over the fabric. This is especially visible in active/active clustering, where ingress and egress interfaces can reside on different nodes and transit traffic must cross the fabric link.
Option B is also correct because the fabric link still exists in active/passive clustering for cluster data-plane synchronization and inter-node state handling, even though active/passive designs minimize fabric transit traffic because only one node normally forwards traffic at a time. Juniper specifically states that active/passive mode minimizes traffic over the fabric link, not that the fabric link is unused.
Options C and D are not the intended answers. The cluster is identified by a configured cluster ID, and each chassis is identified by a node ID, but the fabric interface names themselves are not where the cluster ID is reflected. Reference topics: HA Clustering, fabric link, active/active clustering, active/passive clustering, session synchronization, inter-node traffic.
