DHCP

Dynamic Host Configuration Protocol (DHCP) is an Internet standard for passing configuration information to hosts on a Transmission Control Protocol/Internet Protocol (TCP/IP) network. DHCP is an extension of the Bootstrap Protocol (BootP).

DHCP is used to provide network devices with automatic configurations. When you configure a Shiva® device to use DHCP, you enable dynamic, centralized management of the dial-in IP addresses on your local Internet so you no longer need to assign and track dial-in IP addresses manually.

See the following topics:

DHCP Prerequisites

Shiva's DHCP Implementation

Shiva's DHCP Restrictions

IP Address Leases

Additional Information

Round Robin Server List

Dynamic Reconfiguration

DHCP Prerequisites

To use DHCP, you need:
1.One or more DHCP servers on the network
2. A pool of IP addresses configured in the DHCP server
3. Valid dial-in clients. For example:
4.ShivaRemote for DOS
5.Windows* (Windows* 3.1, Windows* 95, Windows NT*)
6.OS/2 (using IBM* DIALs)
7. Apple* Remote Access* (ARA) 1.0 and 2.0, using
8. MacTCP* MacPPP and InterPPP
9. MacSLIP and SLIP

Note: Intel® Network Systems recommends that the dial-in client does not run DHCP. However, a dial-in client running DHCP can dynamically receive an IP address from a Shiva device acting as a DHCP proxy. This is the same as for dial-in clients that are not running DHCP.

Shiva's DHCP Implementation

Shiva's DHCP implementation lets a Shiva device:
1. Obtain IP addresses and configuration information from a DHCP server (or servers) on the local Internet
2. Provide those addresses and associated configuration information to dial-in clients.

A Shiva device functions as a DHCP client and as a DHCP proxy for the dial-in client. When the dial-in client uses an IP connection to dial in to a Shiva device, the device obtains a lease on the IP address from the DHCP server and passes the IP address to the dial-in client.
The Shiva device, not the dial-in client, renews the IP address lease. This address lease is valid for a configurable time period. Depending on the DHCP implementation on the dial-in client, the remote IP stack should assume that it has an infinite lease for that address.
The Shiva device does not forward DHCP packets that it receives from dial-in clients onto the local area network (LAN).

Shiva's DHCP Restrictions
The following restrictions apply to the Shiva DHCP implementation:

LAN-to-LAN connections do not support DHCP. Each Shiva device in a LAN-to-LAN connection that supports IP must use its own IP address.

A Shiva device cannot use DHCP to get its own IP address. Use Shiva® Net Manager, Shiva® Configurator, Shiva Net Manager for UNIX*, the command shell, the LCD User Interface, or BootP to configure a Shiva device's IP address

The DHCP Overload option (52) is not supported.

There is no option concatenation when multiple occurrences of an option appear in the option list.

When the DHCP server renews an IP address lease and sends option information to a Shiva device that is different from the option information sent earlier, the Shiva device does not pass the new option information to the dial-in client

IP Address Leases
The DHCP server uses one of the following methods to assign IP address leases:

The DHCP server leases the IP address to a Shiva device based on the dial-in user name. By leasing IP addresses based on the dial-in user names, the DHCP server offers the advantage of allowing dial-in users to retain their IP addresses between sessions. If dial-in users hang up and reconnect to a Shiva device before the IP address lease expires, the DHCP server assigns the dial-in user the same IP address from the previous session (assuming that the DHCP server has not been reconfigured).
If dial-in users are reconnecting across multiple Shiva device, enable this option for all Shiva device on the Internet. If in doubt, enable this option for all Shiva device on the local internet. Instruct the dial-in users not to use a generic user name such as Guest.

The Shiva device does not prevent multiple users with the same user name from logging on. So, if multiple users log on with the same user name, they might get the same IP address. When this happens, IP access can be sporadic.

The DHCP server leases the IP address to a Shiva device based on the hardware address of the Shiva device if any of the following apply to the network

Dial-in users can share user names (for example, all users can log on as Guest). The network uses a third-party method of authentication (for example, SecurID*) where users share a user name. There are many dial-in users and you want to make users' IP addresses available immediately when users disconnect.

Additional Information
In addition to IP addresses, DHCP can provide the following information to IP dial-in clients:
Addresses of primary and secondary NetBIOS name servers Addresses of primary and secondary Domain Name Servers (DNS)

If dial-in users are running ShivaRemote, a Shiva device passes this information to the client using Microsoft*'s Internet Protocol Communication Protocol (IPCP) extensions. If the Shiva device is not using DHCP, or if the DHCP server does not supply these addresses, then the Shiva device only sends the addresses to ShivaRemote if they are configured in the Shiva device's configuration. Addresses are sent using IPCP, regardless of whether the addresses are configured or are supplied by DHCP.

Round Robin Server List
A Shiva device uses the following process to find an IP address:
1.It communicates with the first DHCP server until that server fails. Communication is only attempted with one server at a time.
2.If the first DHCP server fails, the Shiva device attempts to communicate with the second DHCP server.
3.If the second DHCP server fails, the Shiva device attempts to communicate with the third DHCP server.
4.If the third DHCP server fails, the Shiva device attempts to communicate with the fourth DHCP server, and so on.

The Shiva device does not try all DCHP servers each time. After a successful call has been made, the search for DHCP servers stops. The search does not always start at the first DCHP server. If a timeout occurs during the search for a DCHP server, the Current Server feature starts the next search at the point where the previous search finished.

Note: If the client cannot communicate with any of the configured DHCP servers, it sends a broadcast message looking for another DHCP server on the network. If there are no configured DHCP servers, then the Shiva device uses a broadcast to find a DHCP server. This is the default: it is not necessary to configure any DHCP servers in order for the Shiva device to use DHCP.

Dynamic Reconfiguration
If you change the parameter values in the DHCP section, a Shiva device implements the changes when you download the changes to the device. You do not need to restart a Shiva device to implement the changes.