RFC 1897 IPv6 Testing Address Allocation January 1996 The values for the autonomous system number of an organization's provider can be obtained from that provider, or can be looked up in the "whois" database maintained by the internic.net. RES This field is reserved and must be set to zero. IPv4 Network Address This is based on the current IPv4 routable address for the subscriber which the interface is connected. It is formed by taking the high order 24 bits of the IPv4 address. For example for an IPv4 address (in IPv4 syntax): IPv4 Address ------------ 39.11.22.1 the value to put in this field of IPv6 address is: IPv4 Format Hex ------------ ------ 39.11.22 270B16 This technique for generating values for this field only works for subscribers which have IPv4 subscriber prefixes less than equal to 24 bits long. There may be subscribers using IPv4 addresses with longer subscriber prefixes, but this conflict is expected to be very rare. Subscribers with subscriber prefixes larger than 24 bits should use the remaining bits in the IPv4 prefix as the high order bits in the Subnet Address field. RES This field is reserved and must be set to zero. Subnet Address The Subnet ID identifies a specific physical link on which the interface is located. There can be multiple subnets on the same physical link. A specific subnet can not span multiple physical links. The assignment of values for this field is left to an individual subscriber. One possible algorithm to generate values for this field is to use the bits in the IPv4 address which identify the IPv4 subnet. Hinden & Postel Experimental