Introduction and Overview
Automatic network configuration has been improved with each release of RISC OS:
- RISC OS 3.6 introduced automatic network configuration using AUN network addresses (1.x.y.z).
- RISC OS Select release 1 introduced an option to disable this automatic allocation.
- RISC OS Select release 2 amalgamated this configuration, and the undocumented automatic DHCP configuration into a single configuration handled by the InetConfigure module.
- RISC OS Select release 3 added ZeroConf 'link local address allocation' to the dynamic address allocation.
- RISC OS Select release 4 extends this further by allowing the gateway and resolver addresses to be automatically configured.
The InetConfigure module performs all automatic address configuration facilities when the machine starts up. This facility can be configured from the desktop using the Interfaces configuration tool, or from the command line.
On a CMOS reset the default configuration selects:
- Dynamic address allocation (DHCP and ZeroConf)
- Enables automatic gateway discovery
- Enables automatic resolver discovery
- Enabled automatic AUN network mapping
Technical Details
Dynamic network configuration
With Select 3, the selection of 'Dynamic' IP addresses will also invoke support for ZeroConf link local addressing. ZeroConf is a networking address configuration system designed by a group focused on interoperability between networked devices. It is used by various computer systems under different names. Under Windows it is known as 'Automatic private address' configuration. On Apple systems, ZeroConf underlies its 'Bonjour' (previously known as 'Rendezvous') implementation.
When activated ZeroConf will configure a private address on an aliased interface. The address configuration will not clash with other addresses on the same network and can be used safely. Should another system be connected to the local network using the same address as a ZeroConf system it will back off and reconfigure to use another address. ZeroConf will always use aliased interface 9.
In the event that no DHCP server is present on the local network the system will still have a ZeroConf (link local) address with which it may communicate with other hosts. As the link local address is never removed (except in the case of an address collision, which can only be caused by two separate networks being connected), connections established through the link local address will not become invalid if a DHCP appears on the network.
Automatic resolver configuration
The automatic resolver configuration uses a number of methods to locate a resolver on the local network. This should allow most systems which use a single gateway with a proxy DNS to discover their network address. The automatic resolver configuration will attempt to probe systems within the network to locate a DNS server. Depending on the DNS server's configuration, this may not locate the server. There is no defined way to perform this automatic resolver configuration and so the implementation is a best effort which should be suitable for most users.
If DHCP is in use and provides a resolver address, it will override the automatic configuration.
Automatic gateway configuration
The automatic gateway configuration uses the standard 'Router Discovery' protocol to locate a system on the local network which provides a router. The deployment of systems which provide a Router Discovery service is limited, but should increase as the functions of home gateways are expanded.
Automatic AUN network mapping
The AUN system implemented by NetI can be configured (separately, through *Configure NetIAutoMap) to automatically map the network addresses assigned to the local interfaces into AUN Network Mappings. See the AUNIntro document for more details about AUN networks.
*Commands
This command configures what automatic configuration will be applied to the first ethernet interface. The configuration is selected with one of:
| Option | Meaning |
|---|---|
| None | No interface configuration |
| AUN | AUN address configuration (1.x.y.z) |
| Dynamic | DHCP interface configuration |
| Static | Static address configuration using the supplied address and network mask prefix in bits (eg 192.168.0.100/24) |
and the resolver and gateway may be given with:
| Option | Meaning |
|---|---|
| DNS address | Configures the default resolver to the given address |
| DNS auto | Configures the default resolver to be automatically discovered |
| GW address | Configures the gateway (default route) to be the given address |
| GW auto | Configures the gateway to be automatically discovered |
We recommend that in most network circumstances the configuration be left set to 'dynamic' and no manual configuration be made.