+.TP
+.B cluster_master_min_adv
+Determines the minumum number of up to date slaves required before the
+master will drop routes (default: 1).
+.TP
+.B ipv6_prefix
+Enable negotiation of IPv6. This forms the the first 64 bits of the
+client allocated address. The remaining 64 come from the allocated
+IPv4 address and 4 bytes of 0s.