NANOG's DHCP and DNS servers are configured for (secure) dynamic DNS updates (based on the Secure Dynamic DNS Howto). When you get a DHCP lease, the DHCP server may (depending on your configuration) update NANOG's DNS zones.

NOTE: If you don't care anything about dynamic DNS updates, thats okay. You can ignore this document and still use the NANOG network as before.

What happens here depends on the way your DHCP client is configured. The variables are:

• Whether or not your DHCP client sends a hostname to the DHCP server.
• Whether or not the hostname is fully qualified.
• Whether or not your DHCP client wants the DHCP server to update the forward zone.

Given these variables, one of three things will happen:

1) If your DHCP client does not provide a hostname, the DHCP server creates a hostname based on your MAC address. It will look like this:

eth-0-90-27-3c-47-b3.dhcp.nanog27.merit.net.

2) If your DHCP client provides a fully qualified hostname and tells the DHCP server that it will update the forward zone itself, the DHCP server does not attempt to update any forward DNS zones (A records).

NOTE: In order to be fully qualified, the name must have more than one component, and end with a dot ("."). For example:

foo	Not fully qualified
foo.com	Not fully qualified
foo.com.	Fully qualified

3) In all other cases, the DHCP server takes the first component of your hostname, and adds it to the dhcp.nanog27.merit.net. zone. For example, if your laptop is called "imac" or "imac.myisp.net," the DHCP server inserts a record for the following hostname:

imac.dhcp.nanog27.merit.net.

The DHCP server updates the reverse zone only if the forward-zone update is successful (or if the client provides a fully qualified name and said it will do the forward-zone update itself).

The following reverse zones are updated by the NANOG DHCP server:

• 165.35.192.in-addr.arpa.
• 166.35.192.in-addr.arpa.
• 167.35.192.in-addr.arpa.

If you are using ISC's dhclient program, you can control its behavior by editing /etc/dhclient.conf. Most likely, you'll want to use this configuration:

send fqdn.fqdn "myhostname";
send fqdn.encoded on;
send fqdn.server-update on;

With the above configuration, the NANOG DHCP server updates the forward zone (dhcp.nanog27.merit.net) and the reverse zone with my.host.name.

In this case, the DHCP server creates an A record for myhostname.dhcp.nanog27.merit.net. and a PTR record with that name for your IP address.

send fqdn.fqdn "my.host.name.";
send fqdn.encoded on;
send fqdn.server-update off;

Then, the NANOG DHCP server only updates the reverse zone, and assumes that your system will do the forward zone update itself.

Dyanmic DNS Updates are usually enabled by default on Windows systems. You can use the DNS control panel to enable or disable DNS updates:

Mac OS seems to have dynamic DNS update enabled by default, but I have no idea how to configure it. Most likely, you'll end up with a name of the form somename.dhcp.nanog27.merit.net.