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update docs about related hosts feature

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Thomas Waldmann 2014-09-26 01:15:24 +02:00
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@ -142,6 +142,74 @@ If your DNS hoster does not support dynamic updates, there is some trick how you
At the nsupdate.info site, add a host "updatedhost.nsupdate.info" and keep it updated using an update client.
Related Hosts
-------------
In short: update a whole bunch of DNS records for other hosts on same LAN.
This is a feature most interesting for IPv6 users, but the same mechanism also
works for IPv4 (it is just rather rare that you get a IPv4 network and you need
dynamic DNS). So, let's assume IPv6 from now on.
On your main host entry you can configure the IPv6 prefix length (think of netmask).
Usually you'll get a /64 network from your ISP, so keep the default of "64" there
and only change it if you know better.
The specific prefix you get from your ISP might be static or may change now and
then (for better privacy or other reasons - and in that case, you really need
the related hosts feature).
You need to configure a dyndns2 compatible updater on some device on your LAN
and the updater needs to send this device's global IPv6 address to the service.
So far, nothing special, upon receiving an update the service will then update
DNS like this:
::
mainhost.nsupdate.info -> pppp:pppp:pppp:pppp:iiii:iiii:iiii:iiii
p are prefix parts, i are host/interface parts of the address.
Additionally, the service will go over all related hosts entries for mainhost
and does more DNS updates based on this computation:
::
relatedhost.mainhost.nsupdate.info -> pppp:pppp:pppp:pppp:rrrr:rrrr:rrrr:rrrr
You also see it prepends the related host's name to your mainhost's FQDN.
For the related hosts's address, p is same prefix as above (the host is on same
network), but r comes from what you entered as interface ID into the related
host record.
In other words:
::
related_fqdn = relatedhost_name.mainhost_fqdn
related_address = mainhost_address_prefix + interface_id
Note:
* enter the static interface ID (usually you can get it from the rear 4 words
of the address that looks like FE80::rrrr:rrrr:rrrr:rrrr). The r part is
usually derived from your hardware MAC address and does not change.
* make sure your device has a IPv6 address with global scope, some prefix that
starts with a "2" and precisely that rrrr:rrrr:rrrr:rrrr value
* you only need a dyndns2 updater on one device (called mainhost in this
example), but the updater needs to find out an address with the same prefix
as seen on your LAN (should be easy if the updater runs on a LAN device, but
might be difficult if it runs on the router and the router has a different
external prefix)
* if you want your mainhost to resolve correctly to some specific device,
make sure you send this device's IPv6 address with the update (myip=...) or
run the updater on that device and make sure the request originates from
the IPv6 address you want in DNS.
Other Services Updaters
-----------------------