Specifies the protocol ID of the route.
Options:
1. direct(1) -indicates the IPv6 direct route
2. static(2) -indicates the IPv6 static route
3. ospf(3) -indicates the IPv6 OSPF route
4. isis(6) -indicates the IPv6 IS-IS route
5. rip(7) -indicates the IPv6 RIP route
6. bgp(8) -indicates the IPv6 BGP route