route source. This parameter can contain one or more
route source identifiers. If the route source is in this
bit map, then a route from that source that meets the other
criteria of this filter will match the filter.
bit 0 bit 31
+---------------------------------------+
| |
+---------------------------------------+
bit31 DIRECT
bit30 STATIC
bit29 RIP
bit28 OSPF
bit27 EGP
bit26 BGP