Rule types:

The RPDB may contain rules of the following types:

• unicast -- the rule prescribes to return the route found in the routing table referenced by the rule.
• blackhole -- the rule prescribes to silently drop the packet.
• unreachable -- the rule prescribes to generate a ``Network is unreachable'' error.
• prohibit -- the rule prescribes to generate ``Communication is administratively prohibited'' error.
• nat -- the rule prescribes to translate the source address of the IP packet into some other value. More about NAT is in Appendix C, p..