This attribute specifies the OSPF tag.
When this attribute is set to a value other than the default value
FFFFFFFF in hex, the protocol attribute must be set to either ospf
or to all. And this more specific route will be advertised together
with the aggregated route only if its OSPF tag matches this
value.
The default tag value 4294967295 (FFFFFFFF in hex) indicates that
the tag is not specified.