Junos OS allows fabric-bound packets to take a new fabric loopback path, freeing up the WAN bandwidth and thus improving the sampling and tunneling performance of the router. You can configure fabric-side loopback by using the fabric loopback wan off statement or switch to WAN side by using the fabric loopback wan on statement at the [edit chassis fpc slot-number] hierarchy level. By default, Junos OS uses fabric loopback for the loopback packets.
