[libvirt] libvirtError: internal error cannot create rule since ebtables tool is missing.

# libvirtd --version libvirtd (libvirt) 0.9.8 # which ebtables /sbin/ebtables 2012-02-15 09:40:59.083+0000: 17675: error : ebtablesCreateRuleInstance:1943 : internal error cannot create rule since ebtables tool is missing. 2012-02-15 09:40:59.107+0000: 17675: error : virNetDevGetIndex:656 : Unable to get index for interface vnet0: No such device ebtables_cmd_path = virFindFileInPath("ebtables"); I can't figure out why ebtables_cmd_path is NULL when