Example: DNS and DHCP on the same System i

 

This example explains how to set up a System i™ model as a Dynamic Host Configuration Protocol (DHCP) server with dynamic Domain Name System (DNS) updates on a simple LAN.

The following illustration depicts how the System i model can act as a DHCP and DNS server for a simple subnet. In this work environment, suppose that the inventory, data entry, and executive clients create documents with graphics from the graphics file server. They connect to the graphics file server by mapping a network drive to its host name.

Figure 1. Dynamic DNS and DHCP

Previous versions of DHCP and DNS were independent of each other. If DHCP assigned a new IP address to a client, the DNS records had to be manually updated by the administrator. In this example, if the graphics file server's IP address changes because it is assigned by DHCP, then its dependent clients are unable to map a network drive to its host name because the DNS records contain the file server's previous IP address.

With the current DNS server, you can dynamically update your DNS records in conjunction with intermittent address changes through DHCP. For example, when the graphics file server renews its lease and is assigned an IP address of 10.1.1.250 by the DHCP server, the associated DNS records are updated dynamically. This allows the other clients to query the DNS server for the graphics file server by its host name without interruption.

You can configure DHCP to update resource records on address mapping (A) records and reverse-lookup pointer (PTR) records on behalf of a client. The A record maps a client's host name to its IP address. The PTR record maps a client's IP address to its host name. For each record that is updated dynamically, an associated text (TXT) record is written to identify that the record was written by DHCP. You can choose to let DHCP update both A and PTR records, or just PTR records. For more information about how to configure DNS to accept dynamic updates, refer to Example: DNS and DHCP on the same System i in the DNS topic collection.

If you set DHCP to update only PTR records, configure DNS to allow updates from clients so that each client can update its A record. Not all DHCP clients support making their own A record update requests. Consult the documentation for your client platform before choosing this method.

To enable DNS updates, create a DNS key for your DHCP server. The DNS key authorizes the DHCP server to update the DNS records based on IP addresses it has distributed. Then, in the DHCP configuration, choose the scope level where you want DNS updates to occur. For example, if you want all subnets to perform DNS updates, set the updates at the Global level. If you want only one subnet to perform updates, then set only that subnet to update.

 

Planning the DHCP setup when using Dynamic DNS

Table 1. Global configuration options (applies to all clients served by the DHCP server)

Object		Value
Configuration options	option 1: Subnet mask	255.255.255.0
	option 6: Domain name server	10.1.1.10
	option 15: Domain name	mycompany.com
Is the system performing DNS updates?		Yes -- Both A and PTR records
Is the system supporting BOOTP clients?		No

Table 2. Subnet for Network Ring

Object		Value
Subnet name		NetworkSubnet
Addresses to manage		10.1.1.250 - 10.1.1.254
Lease time		24 hours (default)
Configuration options	Inherited options	Options from Global configuration

 

Other setup:

Authorize DHCP to send updates to DNS. Refer to Example: DNS and DHCP on the same System i in the DNS topic collection.

 

Parent topic:

Examples: DHCP