DHCP

Name

DHCP -- Dynamic Host Configuration Protocol.

Description

The acronym DHCP stands for Dynamic Host Configuration Protocol. This is a client-server based protocol which allows clients on a TCP/IP network to obtain their configuration parameters from a server.

The protocol supports the transfer of a wide range of configuration parameters such as the client's IP address, netmask, DNS and gateway addresses, plus TCP/IP parameters such as MSS, but is most commonly used to allocate dynamic IP addresses to clients.

IP addresses are "leased" to clients for a period of time, after which the client must renew the lease. Servers generally attempt to re-assign the same IP address to the same client.

DHCP in Xrouter

XRPi includes a DHCP client, and a DHCP server may be included in future, if the need arises. The full range of configuration options is not supported, since in most XRPi application scenarios they are not required. The options currently supported are client's IP address and lease time, DNS and gateway IP addresses.

Lease negotiation and renewal are completely automatic, and the sysop need not be concerned with the process.

Do you need DHCP?

If you wish to connect XRPi to an ISP via a cable modem, e.g. to use it as an Internet Connection Sharing router, you will probably need DHCP if your ISP uses dynamic IP addressing. However, if your ISP assigns you a static IP address you won't need DHCP.

You will not need DHCP if your connection to the ISP is via dial-up PPP, because dynamic IP addresses are assigned as part of the PPP negotiation process.

*** The above scenarios date back to the time when domestic routers had not yet become commonplace, when Windows "Internet Connection Sharing" was in its unreliable infancy, and XRouter was running on DOS machines. Nowadays, with modern ADSL and cable routers, and proper TCP/IP built into Windows, it is unlikely that XRPi would be required to provide the Internet Connection Sharing service. As a matter of interest however, the author is still using DOS XRouter with a cable modem for this purpose! ***

The only reason you might wish to use DHCP these days is to obtain a dynamic LAN IP address from your domestic router, but this is not recommended practice. It is far better to use static IP addresses when feasible, especially when you are "port-forwarding" TCP and UDP ports to specific machines.

You do not need DHCP for normal amateur radio operations.

Enabling DHCP

In XROUTER.CFG, put "DHCP=1" in the appropriate port definition block. There is no need to specify a port IPADDRESS because one will be assigned by the DHCP server. If however, a port IPADDRESS is specified (or it is not specified but a global IP address is specified), that address will be used for non-DHCP traffic until DHCP succeeds in leasing a (possibly different) address. If the global IPADDRESS is 0.0.0.0 or not specified, it will be assigned by the first client which obtains a lease.

To disable DHCP, put "DHCP=0" in the PORT definition block, or simply omit the keyword altogether.

The DHCP command displays DHCP status information, and is detailed in DHCP(2).

See also

DHCP(2) -- DHCP Commands.
XROUTER.CFG(8) -- Main Configuration File.