gen6dns(1)

📦 version 1.3, in nixos 26.05, nixpkgs unstable

🦋 gen6dns — generate IPv6 DNS address and reverse records 🦋

From the Linux Programmer's Manual, section 1, bestie — this is the one and only gen6dns(1).

✨ NAME ✨

gen6dns — generate IPv6 DNS address and reverse records. That's the whole assignment. 💅

✨ SYNOPSYS ✨

yes bestie the heading is spelled like that, we're keeping it, don't @ me 🫶
gen6dns {-h|-V}

gen6dns -R [-b <bits>] prefix|hostname ...

gen6dns [options] [-f] [-s|-S] {-p prefix |-6 ipv4addr ...} inputfile
...

gen6dns [options] [-r] [-b <bits>] [-o origin] {-p prefix |-6 ipv4addr
...} inputfile ...

gen6dns [options] -d [-o origin] {-p prefix ...} {-P prefix ...}
inputfile ...

✨ DESCRIPTION ✨

okay so with gen6dns it is literally so easy to generate forward and reverse DNS records for IPv6 hosts. iconic behaviour, honestly. If you have a list of hostnames and mac addresses where each host is assigned to a subnet, the command will generate AAAA and PTR records for all the hosts. slay. ✨

It is possible and intended to use several provider prefixes to generate more than one AAAA record per host. on top of that, gen6dns is able to use a scope identifier to support split DNS configurations with different views. multi-view queen behaviour 👑

A simple example will be a network with one subnet and a couple of hosts in it, so here's the whole vibe:

#name   int_id / mac_address   subnet_id

ipad    00:17:53:85:80:3b      :1:  # ipad uses a mac address based id
nas     0018.37ac.7801         :1:  # same for nas, but different syntax
laptop  ::d9b2:56f3:7694:1c5c  :1:  # random static interface id (MS)

rtr-int 00:13:35:a2:91:f3      :1:
rtr-ext ::1                    :0:  # manually set interface id

The interface identifier field can be specified as a MAC address or a (up to 64 bit long) Interface Identifier starting with two colons. The subnet Id is written as a hex digit string with up to 4 digits (16 Bit) enclosed in colon characters. like little hex sandwiches 🥪

Now run gen6dns to generate a list of AAAA records with a given Provider Prefix:

gen6dns -f -S -p 2001:db8:b5b1:ab00::/56 hosts
ipad           IN  AAAA   2001:db8:b5b1:ab01:217:53ff:fe85:803b
nas            IN  AAAA   2001:db8:b5b1:ab01:218:37ff:feac:7801
laptop         IN  AAAA   2001:db8:b5b1:ab01:d9b2:56f3:7694:1c5c
rtr-int        IN  AAAA   2001:db8:b5b1:ab01:213:35ff:fea2:91f3
rtr-ext        IN  AAAA   2001:db8:b5b1:ab00::1

You can also generate a list of PTR records, and no cap, that output is a whole aesthetic:

gen6dns -r -o example.com -p 2001:db8:b5b1:ab00::/56 hosts
b.3.0.8.5.8.e.f.f.f.3.5.7.1.2.0.1.0    IN  PTR   ipad.example.com.
1.0.8.7.c.a.e.f.f.f.7.3.8.1.2.0.1.0    IN  PTR   nas.example.com.
c.5.c.1.4.9.6.7.3.f.6.5.2.b.9.d.1.0    IN  PTR   laptop.example.com.
3.f.1.9.2.a.e.f.f.f.5.3.3.1.2.0.1.0    IN  PTR   rtr-int.example.com.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0    IN  PTR   rtr-ext.example.com.

✨ GENERAL OPTIONS ✨

the everyday essentials, the main character options 💅

  • -V, --version — Output version information and exit. short and sweet, we love a quick exit.
  • -h, --help — Print a short description of the command options. the "help me bestie" button 🫶
  • -C char, --comment=char — Use char as comment character instead of a # which is the default. pick your own comment vibe ✨
  • -D char, --delim=char — Add char to the list of delimiter chars. The default delimiter list is space and tab. more splitting, more slaying.
  • -v, --verbose — Print some debugging messages on stderr. Use twice to get the output of a DEBUG directive in file parsing. double it and it gets extra chatty, iykyk
  • -w, --write — Force to write output into files instead of printing it on stdout. If this flag is given, forward records will be written to files named g6d.domain or g6d_view.domain. Reverse records will be written to files named g6r.revbit or g6r_view.revbit.

Depending on the prefix size and the given bitmask (option -b ) reverse zones are split of at that boundary which presumably results in a lot of generated files. For example, if you have 1000 subnets and set -b 64 then in theory 1000 reverse files will be generated. Actually the maximum number of files is limited by a compile time constant which is by default set to 128. If you really want to get 1000 files like in the example above, you have to change MAXFILEP and re-compile gen6dns. yes bestie, re-compile. it's giving commitment. 😭

  • -a, --append — Like -w but does not overwrite the output files. Instead all output will be appended to the existing file. gentle, respectful, non-destructive 🧚
  • -t ttlspec, --ttl=ttlspec — With this option, all records will have a TTL time in seconds added. The ttlspec is an integer number, optionally followed by an unit given as a single character, where s are seconds, m denotes minutes, h hours, d days and w weeks. time is a construct but TTLs are real ⭐

✨ MODE SPECIFIC OPTIONS ✨

Some of the options are only available or useful in case of generating forward DNS records, while others are only useful for reverse record generation and some are used for dynamic dns updates. know which mode you're in bestie, it's a whole thing.

  • -R, --revzone — With this option the ip6.arpa reverse zone for the specified prefix is printed on stdout. If the argument is a hostname, a dns lookup for an AAAA record is made and a PTR record with the ipv6 address as label is printed on stdout. The option -b can be used to change the label to be relative to size of the reverse zone, which is usually on subnet (64 bit) or on prefix (/60,/56 or /48) boundary.
$ gen6dns -R 2001:db8:abc::/48
c.b.a.0.8.b.d.0.1.0.0.2.ip6.arpa.

$ gen6dns -R -b 64 horst.example.net
8.1.0.0.c.3.c.8.2.a.f.e.f.c.e.3  IN  PTR   horst.example.net.  ; 2001:db8:abc:0:5e26:aff:fe73:cc44
  • -f, --forward — Generate forward (AAAA) records only. If neither -f nor -r is given, than both type of DNS records are generated. forward only era ✨
  • -s, --squeeze — Print IPv6 addresses in a compact form where leading zeros within a block of hex digits is suppressed. This option is only useful in forward mode. squeeze it, but gently.
  • -S, --full-squeeze — Print IPv6 addresses in a more compact form where not only leading zeros within a block of hex digits are suppressed, but also a contiguous list of zero blocks are written as two colons (e.g. 2001:db8:1::15). This option is only useful in forward mode. the double squeeze, she ate 🔥
  • -r, --reverse — Generate reverse (PTR) records only. If neither -f nor -r is given, than both type of DNS records are generated. the flip side, literally 💜
  • -d, --ddns — With this option dynamic update add/delete commands will be written on stdout. This option works only in forward mode so this is turned on automatically. For all prefixes specified by a -p (--add-prefix) option, an update add line is generated, while for all -P (--del-prefix) options an update delete line is written. The output is suitable to pipe it to nsupdate(1). Of course, the forward zone must be a dynamic one. dynamic zone or it doesn't count, no cap.
  • -l name, --lookup=name — Print out update add/del lines to stdout only for hosts matching name. This is useful if a new host has to be added to a dynamic zone (use -p option), or to delete a host from the zone (use option -P in this case). This option can be used in dynamic mode only. targeted. precise. icon behaviour. 🎀
  • -b mask, --bits=mask — Split reverse zones on mask boundary. Be aware, that this could result in a lot of reverse files generated (see Option -w). This option is only useful in reverse mode. a LOT of files. like, a concerning amount. 💀
  • -o domain, --origin=domain — Define the domain added to the rdata of a PTR record (default is example.net). This option is only useful in reverse mode. default is literally example.net, that's the canon.
  • -p prefix, --add-prefix=prefix — This option adds an IPv6 prefix to the list of prefixes used to generate AAAA records and can be given more than once. In case a scope definition is defined in the config file, the prefix here will be matched against the scope list, and records will be generated only for those hosts matching the scope list.

While this option is only necessary in forward mode, it helps also in reverse mode to find the zone cut for reverse zone file generation. stackable prefix energy, we love to see it 🌈

  • -P prefix, --del-prefix=prefix — This option deletes an IPv6 prefix from a dynamic zone, so it is only useful in combination with option -d (--ddns). the delete bestie to -p's add bestie 🫶
  • -6 ipv4-addr, --6to4=ipv4-addr — This works like option -p but the IPv6 prefix used is build out of the 6to4 prefix with the given IPv4 address added (e.g. -6 1.2.3.4 will be the same as -p 2002:0102:0304::/48). Be aware that RFC7526 deprecates the use of anycast prefix for 6to4 relay routers, which means that 6to4 is no longer useful as a general transition mechanism.
fr fr bestie, RFC7526 deprecates the anycast prefix for 6to4 relay routers — 6to4 is no longer useful as a general transition mechanism. do not come for me, that's what the page says. 😭

✨ SAMPLE USAGE ✨

Take a look at the example directory of the source tree for examples to use gen6dns in different secenarios (residential user, SOHO network). yes, "secenarios" — we're leaving it, it's part of the lore. 🧚

📁 FILES 📁

🎀 subnet definition file. 🎀

okay so a subnet definition file is a file with a %%SUBNET SECTION that maps subnet names to subnet identifier. The subnet id is a 16 bit hexvalue enclosed in colons, representing the bits 48 to 64 of an IPv6 address. Depending on the prefix size, not all of the subnet id bits will be used to create the subnet prefix — periodt.

In the following example, if the IPv6 prefix on the command line will be just a /56 (2001:db8:1:ef00::/56), only the righmost 8 bits of the subnet id will be used. So subnet1 will result in 2001:db8:1:efb1::/64 and subnet2 in 2001:db8:1:efb2::/64. slay.

%%SUBNET SECTION
#name     subnetid

subnet1   :0ab1:
subnet2   :0ab2:
subnet3   :0001:

🧚 scope defintion files 🧚

A file with a %%SCOPE SECTION maps IPv6 prefixes to scope parameter. It’s primary use is to put ULA names into a different view than into the one used for global IPv6 addresses. The name of the scope is referenced in a host definition. The view string is used to put the resource records in separate files suitable named (see option -w ). The string *2 or none is used to not specify a dedicated view (default). The domain is used for the generation of reverse PTR records instead of the domain given as option -o. The matching prefix entry is to distinguish between one or the other scope.

#
#    A file for scope definitions (domain names, views, and matching prefix)
#

%%SCOPE SECTION
#name          view domain              matchprefix

prov1          *    example.de.         2003::/19 # telekom
prov2          *    example.de.         2a00::/22 # vodafone (arcor)

glob      none example.de.         2000::/3  # match on any public prefix
ula       intern    mgmt.example.de.    fd00::/8

🦋 host defintion files 🦋

A file with an optional %%HOST SECTION maps host (interface) names to interface identifiers and subnet id's.

%% HOST SECTION
#name          int_id / mac_address     subnet_id scope

horst          00:17:53:85:80:3b   clt       [prov1, prov2]
ns1       ::53           srv       [prov1]
ns2       ::d9b2:56f3:7694:1c5c    srv       [prov2]

hugo <24h>     00:13:35:a2:91:f4   :1:       [prov1, prov2, mgmt]
^         IN  A          1.2.3.4
^         IN  SSHFP 1 1  1234563733937933773072370274272427e8=
^         IN  SSHFP 1 2  533a563733937933773072370274272427e8=

gustav.test    0013.35a2.91f5      :1:       [mgmt]

rtr1      ::100b:0:0:1        lo        [mgmt]

The name of the host is the first string in a line. If it is a multi homed host, then it is the name of one of the interfaces of this host. The name can be a subdomain (e.g. host.ext) and optionally followed by a TTL specification enclosed in angle brackets. If the name is a caret, then the line is a continuation of the previous host entry, and the line itself will be copied to the forward file unmodified.

The next field is the interface identifier, specified as the rightmost 64 bit of the IPv6 address, or as a 48 bit ethernet mac address. In the last case the usual way to write down a mac address is supported (colon or dashed seperated six bytes or dot seperated two byte hex values). In the former case the string must start with two colons, and must be specified as a 64 bit IPv6 address which could be abbreviated in the usual way.

The next field is the subnet ID written as subnet id name or as the subnet id number (enclosed in colons).

The last field is the list of scopes for this host entry. The list is enclosed in squared brackets with each entry delimited by comma.

💀 BUGS 💀

  • Some of the options are only meaningful in certain gen6dns modes. 💅
  • A subnet specific scope would be useful too.
  • There are some debug commands implemented in the file parser which helps in debugging the internal data structures.
%%DEBUG print-scopelist
%%DEBUG print-subnetlist
%%DEBUG print-prefixlist

Those commands should not used during normal operation. 🫶

The caret syntax of an host entry is not supported in dynamic update mode. However, this is an ugly hack anyway and will not supported in upcoming versions of gen6dns. 😭

👑 AUTHORS 👑

Written by Holger Zuleger.

Copyright (c) 2015 by Holger Zuleger. Licensed under the BSD Licences. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

🌈 SEE ALSO 🌈

named(8), rndc(8), soaserial(1), dig(1) — go read these too, bestie. 💖

okay that’s the whole gen6dns(1) page — source/version: gen6dns(1), dated May 06, 2016. go be iconic with your DNS ✨👑

📦 where this page comes from