an ipv4 address is 128 bits in length.
how many bits in length is an ipv4 address?
128 bits
bullet::::- if the source ipv6 address is a 6to4 ipv6 address, its corresponding 6to4 router ipv4 address matches the ipv4 source address in the ipv4 encapsulation header,









































bullet::::- similarly, if the destination ipv6 address is a 6to4 ipv6 address, its corresponding 6to4 router ipv4 address matches the ipv4 destination address in the ipv4 encapsulation header,









































bullet::::- any embedded 6to4 router ipv4 address is global unicast.









































section::::6to4 relays.









































section::::6to4 relays.:websites and lists.









































bullet::::- 2008-01-12,19:41:46 archive of public 6to4 relay routers found on earlier http://www.kfu.com/~nsayer/6to4/









































bullet::::- 2012-09-15,13:25:21 archive of time-stamped tables of autonomous systems announcing 6to4 anycast prefixes found on earlier http://bgpmon.net/6to4.php
6to4
normally the border gateway protocol (bgp) used by the provider's routers only looks at the four-octet ip address, but the bgp multiprotocol extensions allow bgp to view the entire 12-octet vpn-ipv4 address, and carry routes from multiple "address families". if the route distinguisher administrator subfield and the assigned number subfield of a vpn-ipv4 address are both set to all zeroes, the vpn-ipv4 address is considered to have exactly the same meaning as the corresponding globally unique ipv4 address. in particular, this vpn-ipv4 address and the corresponding globally unique ipv4 address will be considered comparable by bgp. in all other cases, a vpn-ipv4 address and its corresponding globally unique ipv4 address will be considered noncomparable by bgp. a given per-site forwarding table will only have one vpn-ipv4 route for any given ipv4 address prefix. when a packet's destination address is matched against a vpn-ipv4 route, only the ipv4 part is actually matched.
route distinguisher