IPv6 address predictability

Administrors tend to use IPv6 addresses that are somehow predictable.

One easy location where servers with both IPv4 and IPv6 addresses can be found, is the DNS root zone.  A script looks at some elements of predictability of those IPv6 addresses.
On April 1st 2019, the result was :

$ ./aaaa-predictability
Number of unique AAAA glue records :    3349


Number of AAAA records terminating in ::1  :     433
Number of AAAA records terminating in ::2  :      48
Number of AAAA records terminating in ::3  :      34
Number of AAAA records terminating in ::4  :      23
Number of AAAA records terminating in ::5  :      27
Number of AAAA records terminating in ::6  :      24
Number of AAAA records terminating in ::7  :      19
Number of AAAA records terminating in ::8  :      11
Number of AAAA records terminating in ::9  :     187
Number of AAAA records terminating in ::53 :      75

Number of AAAA records have all but last host byte == 0 :   2796
Number of AAAA records have last two network bytes == 0 :   3315

Number of AAAA records with last network byte == 0 in same /120 :
 164 in 2610:a1:1076::/120
 164 in 2610:a1:1075::/120
 164 in 2610:a1:1074::/120
 138 in 2610:a1:1073::/120
 138 in 2610:a1:1072::/120
 138 in 2610:a1:1071::/120
  85 in 2a04:2b00:13cc::1:/120
  85 in 2001:67c:13cc::1:/120
  71 in 2a04:2b00:13ff::/120
  71 in 2a04:2b00:13ee::/120
  38 in 2610:a1:1076::1:/120
  38 in 2610:a1:1075::1:/120
  38 in 2610:a1:1074::1:/120
  35 in 2a01:618:406::/120
  35 in 2a01:618:402::/120
  35 in 2401:fd80:406::/120
  35 in 2401:fd80:402::/120
  34 in 2001:67c:e0::/120
  29 in 2610:a1:1073::1:/120
  29 in 2610:a1:1072::1:/120
  29 in 2610:a1:1071::1:/120
  28 in 2a01:618:405::/120
  28 in 2a01:618:401::/120
  28 in 2401:fd80:405::/120
  28 in 2401:fd80:401::/120
  24 in 2001:43f8:120::/120
  22 in 2001:678:4::/120
  15 in 2001:678:20::/120
  12 in 2a02:e180:4::/120
  12 in 2a02:e180:3::/120
  10 in 2620:10a:80ab::/120
  10 in 2620:10a:80aa::/120
   8 in 2a01:618:407::/120
   8 in 2a01:618:403::/120
   8 in 2401:fd80:407::/120
   8 in 2401:fd80:403::/120
   8 in 2001:502:ad09::/120
   7 in 2a01:8840:1ba::/120
   7 in 2a01:5b0:4::/120
   7 in 2001:dcd:4::/120
   7 in 2001:dcd:2::/120
   7 in 2001:dcd:1::/120
   6 in 2a01:8840:79::/120
   6 in 2a01:8840:78::/120
   6 in 2a01:8840:77::/120
   6 in 2a01:8840:76::/120
   6 in 2a01:8840:6d::/120
   6 in 2a01:8840:6c::/120
   6 in 2a01:8840:6b::/120
   6 in 2a01:8840:6a::/120
   6 in 2a01:8840:4d::/120
   6 in 2a01:8840:4c::/120
   6 in 2a01:8840:4b::/120
   6 in 2a01:8840:4a::/120
   6 in 2620:171:d01:dc::/120
   6 in 2620:171:a01:ad::/120
   6 in 2001:dcd:3::/120
   6 in 2001:67c:10e0::/120
   6 in 2001:678:24::/120
   6 in 2001:620:0:ff::/120

AAAA records that terminate in IPv4 address (with . --> :) :
              z.nic.no. :    158.38.8.133  &      2001:700:0:52d:158:38:8:133
              a.nic.cl. :   190.124.27.10  &    2001:1398:121:0:190:124:27:10
      primary.rotld.ro. :   192.162.16.18  &      2a03:5e80:0:4:192:162:16:18
       dns-md.rotld.ro. :   192.162.16.19  &      2a03:5e80:0:4:192:162:16:19
    sec-dns-a.rotld.ro. :   192.162.16.20  &      2a03:5e80:0:4:192:162:16:20
              a.nic.bg. :   192.92.129.99  &         2a02:6a80::192:92:129:99
        ns.register.bg. :   192.92.129.99  &         2a02:6a80::192:92:129:99
              s.nic.dk. :  193.176.144.15  &    2a00:d78:0:102:193:176:144:15
          e.ext.nic.fr. :  193.176.144.22  &    2a00:d78:0:102:193:176:144:22
    sec-dns-b.rotld.ro. :  193.230.31.230  &     2a03:5e80:0:5:193:230:31:230
        a.dns.ripn.net. :   193.232.128.6  &      2001:678:17:0:193:232:128:6
        e.dns.ripn.net. :  193.232.142.17  &     2001:678:15:0:193:232:142:17
        f.dns.ripn.net. :  193.232.156.17  &     2001:678:14:0:193:232:156:17
              b.nic.bg. :    193.68.3.232  &          2a02:6a80::193:68:3:232
       ns2.register.bg. :    193.68.3.232  &          2a02:6a80::193:68:3:232
              c.nic.bg. :    193.68.99.99  &          2a02:6a80::193:68:99:99
       ns3.register.bg. :    193.68.99.99  &          2a02:6a80::193:68:99:99
              a.dns.it. :    194.0.16.215  &       2001:678:12:0:194:0:16:215
            ns1.dns.aw. :      194.0.28.2  &         2001:678:2c:0:194:0:28:2
     ns1.nic.amsterdam. :      194.0.28.4  &         2001:678:2c:0:194:0:28:4
       ns1.nic.politie. :      194.0.28.5  &         2001:678:2c:0:194:0:28:5
            ns1.dns.nl. :     194.0.28.53  &        2001:678:2c:0:194:0:28:53
     nameserver.cnr.it. :  194.119.192.34  &  2a00:1620:c0:220:194:119:192:34
        d.dns.ripn.net. :  194.190.124.17  &     2001:678:18:0:194:190:124:17
        b.dns.ripn.net. :   194.85.252.62  &      2001:678:16:0:194:85:252:62
         ns-ext.nic.cl. :    200.1.123.14  &       2001:1398:1:0:200:1:123:14
              b.nic.cl. :       200.7.4.7  &        2001:1398:274:0:200:7:4:7
              c.nic.lk. :    203.143.29.3  &       2405:5400:3:1:203:143:29:3
       john.vatican.va. :    212.77.0.110  &         2a01:b8:0:1:212:77:0:110
    michael.vatican.va. :      212.77.0.2  &           2a01:b8:0:1:212:77:0:2
            ns1.ati.tn. :    41.228.62.63  &    2c0f:fab0:ffff:4:41:228:62:63
            ns2.ati.tn. :    41.228.63.62  &    2c0f:fab0:ffff:5:41:228:63:62
 ns1.liquidtelecom.net. :       5.11.11.1  &             2c0f:fe40::5:11:11:1
 ns2.liquidtelecom.net. :      5.11.11.10  &            2c0f:fe40::5:11:11:10

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