Title:
	DHCP to DNS synchronising service for SME Server

Contributed by:
	Rick Jones <rick@activeservice.co.uk>
	Active Service <www.activeservice.co.uk>

Version:
	1.0 release 1
Date:
	March 2005

Applicable to:
	SME Server version 6.0.x
	(not tested under 6.5, and may not be necessary)

Acknowledgements:
	The idea for this was inspired by Michael Stella's utility
	(www.thismetalsky.org), although I didn't use any of his code
	directly. This is mainly because all the mechanism for dynamically
	building config files already exists in SME's template system, so
	most of Michael's code was irrelevant or needed re-working.
	But thanks for the idea anyway Michael!


Purpose

The standard configuration of tinydns in SME Server 6 supplies hard-coded
names for all IP addresses in the local subnet range. These take the form
"pc-00001", "pc-00002", etc. This particularly affects reverse DNS of local
clients, so local IPs do not resolve to the names they used when registering
in DHCP.

This contrib uses the state of DHCP leases to build the tinydns data file,
so that DNS resolves the registered names and IPs correctly in both
directions. It also continuously monitors the leases, and updates DNS
whenever there is a change. Any statically defined IPs (using MAC addresses
in the Hostnames panel) are also correctly resolved.


Name conflicts

It's quite possible in a dynamic environment (e.g. WiFi with various laptops
coming and going) that name clashes will arise; either a new client with the
same name as a statically pre-configured one, or simply two clients with the
same name. In this case, conflicting clients will have numeric suffixes added
to their DNS names so that the DNS entries are unique.

If a DNS client doesn't report a name, then the MAC address is used as the
host for the DNS entry.

Thanks go to Placido Sanchez for discovering these problems, as well as
suggestions and substantial testing.


Extras

In addition, reverse DNS lookup of the SME server's own IP correctly
resolves to its hostname, rather than "pc-0000x".

Installing this RPM also enables the use of Cname entries for sub-domain
names. To do this, use the Hostnames manager panel to add a hostname of type
"Remote". In the IP address field you can enter the actual hostname of the
machine hosting the sub-domain as an alternative to its IP address (this RPM
removes the usual validation for an IP entry). Saving the changes will then
write a Cname record into the DNS data file.

This feature is useful if you host one or more sub-domains on remote sites
(e.g. an Internet hosting provider) and you need to point to the actual
server. A Cname can be more reliable than an IP, as the provider may change
his IP addresses but is less likely to change the actual host names.


Comments

I hope this works well for you. If you find any bugs or problems, or have
any comments, please email contribs@activeservice.co.uk.


Rick Jones