external route source. This parameter can contain one
or more external route source identifiers. If the external
route source is in this bit map, then a route from that
external 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 BGP