Example: DHCP and PPP profile on different System i models

This example explains how to set up two System i™ models as the network Dynamic Host Configuration Protocol (DHCP) server and a BOOTP/DHCP relay agent for two LANs and remote dial-in clients.

The example about PPP and DHCP on a single System i model shows how to use PPP and DHCP on a single system to permit dial-in clients access to a network. If you are concerned with the physical layout of your network or with security, it might be better to have the PPP and DHCP servers separated or to have a dedicated PPP server without DHCP services. The following figure represents a network that has dial-in clients with the PPP and DHCP policies on different servers.

Figure 1. DHCP and PPP profile on different System i models

The remote data entry clients dial into the System i PPP server. The PPP profile on that server must have a remote IP address method of DHCP, such as in the example about PPP and DHCP on a single System i model as well as IP forwarding in the PPP profile and in the TCP/IP stack properties. Furthermore, because this server is acting as a DHCP relay agent, the BOOTP/DHCP relay agent must be on. This allows the System i Remote Access server to pass on DHCP DISCOVER packets to the DHCP server. The DHCP server then responds and distributes TCP/IP information to the dial-in clients through the PPP server.

The DHCP server is responsible for distributing IP addresses to both the 10.1.1.0 and 10.1.2.0 networks. In the data entry network, the DHCP server gives out IP addresses from 10.1.2.10 to 10.1.2.40 to either dial-in or directly attached network clients. The data entry clients also need a router address (option 3) of 10.1.2.1 to communicate with the work network, and the System i DHCP server must also have IP forwarding enabled.

Also, the Local Interface IP address in the PPP profile must be an IP address that falls within the subnet definition in the DHCP server. In this example, the PPP profile Local Interface address should be 10.1.2.2. This address should also be excluded from the DHCP server's address pool so that it is not assigned to a DHCP client. The Local Interface IP address must be an address to which the DHCP server can send reply packets to.

Planning the DHCP setup for DHCP with a DHCP relay agent

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	10.1.1.1
	option 15: Domain name	mycompany.com
Is the system performing DNS updates?		No
Is the system supporting BOOTP clients?		No

Table 2. Subnet for Work Network
Object		Value
Subnet name		WorkNetwork
Addresses to manage		10.1.1.3 - 10.1.1.150
Lease time		24 hours (default)
Configuration options	Inherited options	Options from Global configuration
Subnet addresses not assigned by server		none

Table 3. Subnet for Data Entry Network
Object		Value
Subnet Name		DataEntry
Addresses to manage		10.1.2.10 - 10.1.2.40
Lease time		24 hours (default)
Configuration options	option 3: Router	10.1.2.1
Configuration options	Inherited options	Options from Global configuration
Subnet addresses not assigned by server		10.1.2.1 (Router) 10.1.2.15 (Remote Data Entry client's local interface IP address) 10.1.2.14 (Remote Data Entry client's local interface IP address)

Other setup on a System i platform running PPP

Set up the BOOTP/DHCP relay agent TCP/IP server

Object Value

Interface address 10.1.2.2
Relay packets to Server IP address 10.1.2.1
Set the Remote IP address method to DHCP in the PPP receiver connection profile
1. Enable DHCP WAN client connection with a DHCP server or relay connection using the Services menu item for Remote Access Services in iSeries™ Navigator
2. Select to Use DHCP for the IP address assignment method under the TCP/IP Settings Properties of the Receiver Connection Profile in iSeries Navigator
Allow remote system to access other networks (IP forwarding) under the TCP/IP Settings Properties of the Receiver Connection Profile in iSeries Navigator (to allow the remote clients to communicate with the data entry network)
Enable IP datagram forwarding under the Settings Properties of the TCP/IP Configuration in iSeries Navigator (to allow the remote clients to communicate with the data entry network)

Object	Value
Interface address	10.1.2.2
Relay packets to Server IP address	10.1.2.1

Parent topic:

Examples: DHCP

Related reference
Example: PPP and DHCP on a single System i