# Specifying the router as a candidate BSR on a VLAN interface

Because PIM-SM cannot run without a bootstrap router (BSR), you must specify at least one C-BSR in the domain. Any additional C-BSRs provide backup protection in case the primary BSR fails.

The C-BSR with the highest configured priority becomes the BSR for the domain. If two C-BSRs have equal priority, the candidate with the higher IP address becomes the BSR. If you add a new C-BSR with the highest priority to the domain, it automatically becomes the new BSR.

With the Ethernet Routing Switch 5000 Series, you can configure every PIM-enabled interface as a C-BSR.