icture a maintenance technician on the night shift. A device on the Ethernet network fails and the production line goes down. First the device must be located physically and then identified by type and model number. Then it’s off to the crib to find a replacement. If all goes well, sufficient information is gathered and an appropriate spare is located. Perhaps this is accomplished in less than an hour. Meanwhile the line is still down.
With the device ready to be installed, the technician looks for the dipswitches to set the network address and suddenly realizes that this is an Ethernet network, meaning that the device requires an Internet Protocol (IP) address. With luck, the address may be written on the old part. If not, it must be located. Then, how is the device configured? Perhaps the supplier used Bootstrap Protocol (BootP) or a special serial cable and software.
Network Vision, a Newburyport, Mass., company specializing in Ethernet solutions, has developed a solution, called Auto-IP, which works with the company’s IntraVue networking software. The technician in the above situation would receive an e-mail page from IntraVue at the time of the device failure. The software also provides a network map, making it easy to locate the defective device. After the device is replaced, the Auto-IP manages all devices on the network and provides the correct IP address automatically on power-up.
Mark Fondl, Network Vision president, contends, “The use of commercial technology not only reduces the cost of equipment, but also deployment. IntraVue and Auto-IP were specifically developed to handle the unique requirements of the industrial environment.”
IntraVue software determines the exact location of every device on the network using a process that extracts data from the switches and applies the data to a unique algorithm that automatically draws the network connections, including hubs and unmanaged switches. The software then continuously monitors the network, to determine exactly what has occurred, and prompts the appropriate response.
BootP leverages the fact that the physical Ethernet address (a.k.a. MAC address) of every device is unique. A computer somewhere on the network (the BootP server) is set up to listen for BootP request packets, which will be broadcast by each device when it starts up. When the BootP request is received, and if there is a “match” in the database, the server will respond with the correct IP address information.
Dynamic Host Configuration Protocol (DHCP) is a later variation of BootP, designed to solve the problem of assigning temporary addresses to devices such as user laptop computers, which frequently “appear” and “disappear” on a network. Instead of maintaining a rigid database in which the MAC address must be pre-registered, as with BootP, a DHCP server instead keeps a pool of addresses, each of which may be “leased” or “free” at any time. However, this dynamic assignment method is not useful for most industrial device networks.
DHCP Option 82 allows end-user devices to classify themselves to the DCHP server, which can allocate them different settings because of their particular needs. The trick is performed by having the managed switch intercept an incoming BootP or DHCP request and note which port the request came from. The DHCP request is forwarded to the real DHCP server elsewhere on the network, where IP address allocations have been previously associated with the Option 82 data.
This method requires special configuration at the switches. It is necessary for the switches to determine which of their ports support Option 82 forwarding, and which should leave the DHCP requests alone.
Auto-IP works through managed switches that support Simple Network Management Protocol (SNMP), and specifically the Bridge MIB defined in RFC1493 (which Fondl contends is most of them). A central management station can therefore report on which port a particular MAC was found. The Auto-IP technique involves a modified BootP server, which is capable of issuing SNMP queries to switches to identify the switch and port number. The server uses this information, along with knowledge of whether a station is currently up or down, to determine whether a newly seen MAC represents a new device or a replacement for an existing one.