<----------------------16 bits----------------->		<----------------------16 bits----------------->
Hardware Type		Protocol Type
HLen	Plen	Operation
Sender Hardware Address
Sender Protocol Address
Target Hardware Address
Target Protocol Address

In the above figure it is clear that RARP and ARP has the same structure:

• Hardware type - which specifies a hardware interface type for which the sender requires a response.
• Protocol type -which specifies the type of the high-level protocol address the sender has supplied.
• Hlen - Hardware address length.
• Plen - Protocol address length.
• Operation - The values are as follows:
  • ARP request.
  • ARP response.
  • RARP request.
  • RARP response.
  • Dynamic RARP request.
  • Dynamic RARP reply.
  • Dynamic RARP error.
  • InARP request.
  • InARP reply.
• Sender hardware address -HLen bytes in length.
• Sender protocol address - PLen bytes in length.
• Target hardware address - HLen bytes in length.
• Target protocol address - PLen bytes in length.

1. RARP (Reverse Address Resolution Protocol) allows a physical machine in a local area network to request its IP address from a gateway server's Address Resolution Protocol (ARP) cache or table.





2. A network administrator creates a table in a local area network's gateway router that maps the physical machine (or Media Access Control - MAC address) addresses to corresponding to the Internet Protocol addresses (IP address).





3. When a new machine is set up, its RARP client program requests from RARP server on the router to be sent its IP address.





4. Assuming that an entry has been set up in the router table and the RARP server will return the IP address to the machine which can store it for future use.





5. RARP is available for Fiber Distributed-Data Interface,Ethernet, and Token Ring LANs and ARP (Address Resolution Protocol) performs the opposite function as the RARP: mapping of an IP address to a physical machine address.

BOOTP sends IP addresses and other configuration data to hosts that broadcast BOOTP requests and because some BOOTP clients require more data to boot than can fit in a BOOTP response, BOOTP provides a means for specifying the location of a boot file. The BOOTP client can then load the file using TFTP (Trivial File Transfer Protocol). Usually, the data in the boot file (such as an X server for an X terminal) is specific to the vendor of BOOTP client software.

The BOOTP service responds to BOOTP requests only and if you are using the BOOTP-only service, DHCP services are not available. The BOOTP server is provided for backwards compatibility for those sites not wishing to change their configurations.

The MultiNet BOOTP (Bootstrap Protocol) service lets your OpenVMS system help other network devices establish network connectivity and diskless hosts. The remote system broadcasts a BOOTP request over the network with its Ethernet address and the BOOTP server looks up the host's address in a configuration file (MULTINET:BOOTP-SERVER.CONFIGURATION) and responds with the host's IP address, subnet mask, gateway address, initial load file, and any other data needed by the client. Using this information, the client can boot from the network itself.

Starting with MultiNet V3.5, MultiNet includes two BOOTP servers: An older server provided for backwards compatibility for those sites not wishing to change their configuration, and a newer DHCP/BOOTP server that provides features not present in the older and BOOTP-only server.

Configuring the BOOTP server involves:

1. Obtaining the data required by each BOOTP client.



2. Starting and enabling BOOTP.



3. Modifying the BOOTP configuration file.



4. Reloading the BOOTP configuration.



5. Disabling debug messages, if desired.

Make a list of configuration parameters (known as BOOTP options) required by devices you want to configure using BOOTP.

Because some network devices require vendor-specific configuration or large amounts of information at boot time, BOOTP lets you specify the path names of additional configuration files the client can download from TFTP servers.

Note! If you are running DNS, make sure you use the same IP address and host name data used by your primary site's DNS servers.

If you are using host tables instead of DNS, make sure you use the same IP address and host name data listed in MULTINET:HOSTS.LOCAL.

• Short for Point-to-Point Tunneling Protocol, a new technology for creating Virtual Private Networks (VPNs) developed jointly by the Microsoft Corporation, U.S. Robotics, and several remote access vendor companies, known collectively as the PPTP Forum.





• A VPN is a private network of computers that uses the public Internet to connect some nodes and because the Internet is essentially an open network, the Point-to-Point Tunneling Protocol (PPTP) is used to ensure that messages transmitted from one VPN node to another are secure.





• With PPTP, users can dial in to their corporate network via Internet.

PPTP allows existing Network Access Server (NAS) functions to be separated using a client-server architecture and traditionally, the following functions are implemented by a NAS:

1. Physical native interfacing to ISDN or PSTN and control of external modems or terminal adapters. A NAS may interface directly to a telco digital or analog circuit or attach via an external modem or terminal adapter. Control of a circuit-switched connection is accomplished with eitherDSS1 ISDN call control or modem control protocols. The NAS, in conjunction with the modem or terminal adapters, may perform rate adaption,sync to async conversion,analog to digital conversion or a number of other alterations of data streams.





2. Logical termination of a Point-to-Point-Protocol (PPP) Link Control Protocol (LCP) session.





3. Participation in PPP authentication protocol .





4. Bundle management and Channel aggregation for PPP Multilink Protocol.





5. Logical termination of the various PPP network control protocols (NCP).





6. Multiprotocol bridging and routing between NAS interfaces. PPTP divides these functions between the PAC and PNS.





7. The protocol used to carry PPP protocol data units (PDUs) between the PNS and PAC, as well as call control and management is addressed by PPTP.