new features: July 2008 Archives

IPv6 RDNS setup

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so IPv6 rdns is a little different from  IPv4 rdns.  With IPv4 rdns, you split each IP address on byte boundries, reverse the octets, and append in-addr.arpa.   all data is represented in decimal, and you don't pad zeros.  for example, to get the ipv4 rdns of 216.218.223.67  you look for a ptr record named 67.223.218.216.in-addr.arpa. 

IPv6 rdns is similar on the surface;   instead of .in-addr.arpa. you append ip6.arpa, but you split the address in unexpected ways, too:

IPv6 addresses are written out in hex, two byte chunks seperated by colon charaters.   IPv6 rdns writes out the full address in hex including padding out all zeros,  and then splits it into 4 bit chunks (single hex characters)  and reverses those. 

so to get the rdns of, say, ns2.prgmr.com,  IPv6 address: 2001:470:1:41:a800:ff:fe50:3143
you would look for a PTR record that looked like this:;  3.4.1.3.0.5.e.f.f.f.0.0.0.0.8.a.1.4.0.0.1.0.0.0.0.7.4.0.1.0.0.2.ip6.arpa.

note that you must pad out the zeros so that each two-byte chunk seperated by the ':' character is represented by four characters.    

Of course, dig -x does this for us....


 dig -x 2001:470:1:41:a800:ff:fe50:3143

; <<>> DiG 9.3.4-P1 <<>> -x 2001:470:1:41:a800:ff:fe50:3143
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 20189
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;3.4.1.3.0.5.e.f.f.f.0.0.0.0.8.a.1.4.0.0.1.0.0.0.0.7.4.0.1.0.0.2.ip6.arpa

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This page is a archive of entries in the new features category from July 2008.

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