Most of the complexity of IPv6 is down at the IP and ICMP layer, the IPng Working Group was not given the task of changing TCP or UDP. However there are some unavoidable application changes. RFC 2133 expands on this.
Host renumbering and the possible use of IPv6 <-> IPv4 gateways causes problems for those pathological protocols which embed their IP address in the data body, ftp is the classic example, it was always a mistake to do this. IPv6 ftp implements a new directive (SPOST) which only sends port numbers, not IP addresses. Other applications with IP addresses embedded in the data stream will probably have to be changed.
In IPv4 you convert an IP address to a host name by reversing the octets, appending 'in-addr.arpa' and doing a name lookup on the result. For example, 18.104.22.168 is looked up as 22.214.171.124.in-addr.arpa. IPv6 address lookups take the 64 bit address, write each hex nibble out in full (no zero removal), reverse it and append 'ip6.int'. 5F04:C500:CB2B:B300::6 maps to 126.96.36.199.0.0.0.0.0.0.0.0.0.0.0.0.0.0.3.b.b.2.b.c.0.0.5.c.4.0.f.5.ip6.int.
DNS has a new record type (AAAA) for name to IPv6 addresses lookups. My router-6 has both IPv4 and IPv6 addresses so it has both A and AAAA records.
router-6 IN A 188.8.131.52 router-6 IN AAAA 5f04:c500:cb2b:b300::6
PTR records are unchanged in format, they just get a lot longer.
; ; origin is 0.0.3.b.b.2.b.c.0.0.5.c.4.0.f.5.ip6.int ; @ IN SOA firewall.ocs.com.au. admin.ocs.com.au. ( 199703191 ; Serial 10800 ; Refresh after 3 hours 3600 ; Retry after 1 hour 604800 ; Expire after 1 week 86400 ) ; Minimum TTL of 1 day ; ; Name server(s) ; IN NS firewall.ocs.com.au. IN NS mail.ocs.com.au. ; ; Host addresses ; 184.108.40.206.0.0.0.0.0.0.0.0.0.0.0.0 IN PTR router-6.ocs.com.au.
© Keith Owens O. C. Software P/L 1997