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Updated: 11 December 1998

OpenVMS I/O User's Reference Manual

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9.7.5.4 Configuring LAST over an Emulated LAN

By default, LAST starts on all adapters, and there is currently no method specifying a specific device to be used.

9.7.5.5 Configuring DECnet over an Emulated LAN

DECnet configures over an emulated LAN like any other LAN device. See the DECnet Phase IV and DECnet-Plus documentation.

9.8 Ports and LAN Configuration

A port in a LAN configuration consists of a protocol type, a service access point (SAP) or protocol identifier, and a controller. There are as many ports on a LAN controller as there are protocol types, SAPs, and protocol identifiers. Each port is independent of other ports running on the same LAN controller.

Application programs use either the LAN driver's QIO interface or VCI interface to perform I/O operations to and from other nodes on the LAN. This chapter describes the QIO interface. Figure 9-2 shows the relationship of most Ethernet controllers to the processor and to the user application program.

Figure 9-2 Typical Ethernet Configuration

9.8.1 Driver Initialization and Operation

The following sequence initializes and starts a port on a LAN device driver:

  1. Use the Assign I/O Channel ($ASSIGN) system service to assign I/O channels to one or more of the LAN device names and devices specified in Table 9-1 and Table 9-2. $ASSIGN creates a new unit control block (UCB), to which the channel for the port is assigned.
  2. Start up the port with the set mode function and startup function modifier (see Section 9.16.3.1). You must supply the required P2 buffer parameters listed in Table 9-16.
  3. Perform read, write, and sense mode operations as needed.
  4. Shut down the port with the set mode function and shutdown function modifier (see Section 9.16.3.4).
  5. Use the Deassign I/O Channel ($DASSGN) system service to deassign the I/O channel.

The sample programs described in Section 9.18.2 illustrate how to perform these procedures for Ethernet and IEEE 802 ports.

9.9 Ethernet Addresses

The LAN is a medium for creating a network; it is not a network by itself. The LAN controller and the local system constitute a node. Nodes on the LAN are identified by unique Ethernet addresses. A message can be sent to one, several, or all nodes on the LAN simultaneously, depending on the Ethernet address used. You do not have to specify the Ethernet address of your own node to communicate with other nodes on the same Ethernet. However, you do need to know the Ethernet address of the node with which you want to communicate.

9.9.1 Format of Ethernet Addresses

An Ethernet address is 48 bits in length. Ethernet addresses are represented by the Ethernet standard as six pairs of hexadecimal digits (six bytes), separated by hyphens (for example, AA-01-23-45-67-FF). The bytes are displayed from left to right in the order in which they are transmitted; bits within each byte are transmitted from right to left. In this example, byte AA is transmitted first; byte FF is transmitted last. (See the description of NMA$C_PCLI_PHA in Table 9-16, Section 9.16.3.1, for the internal representation of addresses.)

Upon application, IEEE assigns a block of addresses to a producer of LAN nodes. Thus, every manufacturer has a unique set of addresses to use. Normally, one address out of the assigned block of physical addresses is permanently associated with each controller (usually in read-only memory). This address is known as the hardware address of the controller. Each individual controller has a unique hardware address.

9.9.2 Ethernet Address Classifications

An Ethernet address can be a physical address of a single node or a multicast address, depending on the value of the low-order bit of the first byte of the address (this bit is transmitted first). Following are the two types of node addresses:

Contrary to the Ethernet specification and the IEEE 802.3 Standard, the broadcast address (FF-FF-FF-FF-FF-FF) must be enabled as a multicast address in order to receive messages addressed to it.

9.9.3 Selecting an Ethernet Physical Address

The OpenVMS interface to the LAN controllers allows you to set a physical address of the controller. The selection of the physical address of a LAN controller is different for CSMA/CD (Ethernet and 802.3) and FDDI.

For CSMA/CD, all users of the controller must agree on this address. The first user of the controller chooses the physical address; any additional users of the controller must specify either the same physical address, no physical address, or change the address (if allowed). When all channels to the controller are shut down, the next user to start a channel chooses the physical address. The controller's physical address is always chosen on the first successful startup when there are no active ports. If the address is not chosen at this time, the controller's hardware address is used as the physical address.

For CSMA/CD, the Can Change Address parameter allows the physical address to be changed even though there are active users. If all current users of the controller have set the NMA$C_PCLI_CCA parameter to NMA$C_STATE_ON, then the physical address can be changed.

For FDDI, each port using a controller may specify its own unique physical address. Any combination of sharing of physical addresses is also allowed across the ports of an FDDI controller. For example, ports A, B, and C may use one unique physical address and ports D and E may use another unique address.

9.9.4 Ethernet Physical and Multicast Address Values

The following are multicast addresses assigned for use in cross-company communications:
Value Meaning
FF-FF-FF-FF-FF-FF Broadcast
CF-00-00-00-00-00 Loopback assistance

The following are commonly used multicast addresses:
Value Meaning
AB-00-00-01-00-00 Dump/load assistance
AB-00-00-02-00-00 Remote console
AB-00-00-03-00-00 Level 1 and Level 2 routers
AB-00-00-04-00-00 All end nodes
09-00-2B-02-00-00 Level 2 routers
AB-00-00-05-00-00
through
AB-00-03-FF-FF-FF 		Reserved for future use
AB-00-03-00-00-00 LAT
AB-00-04-00-00-00
through
AB-00-04-00-FF-FF 		For use by Compaq customers for their own applications
AB-00-04-01-00-00
through
AB-00-04-01-FF-FF 		Local area VMScluster
AB-00-04-02-00-00
through
AB-00-04-FF-FF-FF 		Reserved for future use
09-00-2B-01-00-00 Bridge management
09-00-2B-01-00-01 Bridge hello multicast

9.9.5 Token Ring Functional Address Mapping

Except for the global broadcast address (FF-FF-FF-FF-FF-FF), Token Ring hardware does not support the 802 standard group LAN address mechanism. Instead, it uses functional addresses. These functional addresses are locally administered group addresses (multicast addresses). The first two bytes of the address are always 03-00 (canonical format), and the remaining four bytes contain a bit mask that specifies which of the 32 possible combination masks is being described.

Because most OpenVMS LAN applications use standard multicast addresses, a mechanism has been designed to map functional addresses to globally and locally administered multicast addresses. This allows applications to use the same multicast addresses that are used in the other LAN media.

Table 9-6 shows the default mapping used by the OpenVMS Alpha Token Ring drivers:

Table 9-6 Address Mappings of Token Ring Drivers
Multicast Address Functional Address Bit-Reversed Description
09-00-2B-00-00-04 03-00-00-00-02-00 C0:00:00:00:40:00 ISO 9542 All End-system Network Entites
09-00-2B-00-00-05 03-00-00-00-01-00 C0:00:00:00:80:00 ISO 9542 All Intermediate System Network Entities
CF-00-00-00-00-00 03-00-00-08-00-00 C0:00:00:10:00:00 Loopback Assistance
AB-00-00-01-00-00 03-00-02-00-00-00 C0:00:40:00:00:00 MOP Dump/Load
AB-00-00-02-00-00 03-00-04-00-00-00 C0:00:20:00:00:00 MOP Remote Console
AB-00-00-03-00-00 03-00-08-00-00-00 C0:00:10:00:00:00 DNA L1 Routers
09-00-2B-02-00-00 03-00-08-00-00-00 C0:00:10:00:00:00 DNA L2 Routers
09-00-2B-02-01-0A 03-00-08-00-00-00 C0:00:10:00:00:00 DECnet Phase IV---TRN---All Phase IV---TRN Routers
AB-00-00-04-00-00 03-00-10-00-00-00 C0:00:08:00:00:00 DNA End nodes
09-00-2B-02-01-0B 03-00-10-00-00-00 C0:00:08:00:00:00 Phase IV Prime Unknown
09-00-2B-00-00-07 03-00-20-00-00-00 C0:00:04:00:00:00 PCSA NETBIOS Emulatn
09-00-2B-00-00-0F 03-00-40-00-00-00 C0:00:02:00:00:00 Local Area Transport (LAT)
09-00-2B-02-01-04 03-00-80-00-00-00 C0:00:01:00:00:00 LAT Directory Service Solicit (to slave)
09-00-2B-02-01-07 03-00-00-02-00-00 C0:00:00:40:00:00 LAT Directory Service Solicit---X Service Class
09-00-2B-04-00-00 03-00-00-04-00-00 C0:00:00:20:00:00 LAST
09-00-2B-02-01-00 03-00-00-00-08-00 C0:00:00:00:10:00 DNA Naming Service Advertisement
09-00-2B-02-01-01 03-00-00-00-10-00 C0:00:00:00:08:00 DNA Naming Service Solicitation
09-00-2B-02-01-02 03-00-00-00-20-00 C0:00:00:00:04:00 DNA Time Service
03-00-00-00-00-01 03-00-00-00-00-01 C0:00:00:00:00:80 NETBUI Emulation

If an application needs to change or add mappings, QIOs exist for performing such operations. If the system or network manager has a requirement regarding mapping of the functional addresses, the LAN control program (LANCP) utility may be used to manage the mapping. The following example maps the multicast address AB-01-01-01-02-03 to functional address 03-00-00-01-00-00 on Token Ring device ICA0:. 


$MCR LANCP
LANCP>SET DEVICE/MAP= -
_LANCP>(MULTICAST=AB-01-01-01-02-03,-
_LANCP>FUNCTIONAL=00-01-00-00) ICA0:

Note that it is possible for more than one multicast address to map to the same functional address. In all cases, the use of the functional address is associated with an individual application's protocol.

9.10 Configuring ISA Devices (Alpha Only)

On Alpha systems, the way to configure an ISA LAN device is to type 'isacfg' at the console prompt (>>>). For complete information on using 'isacfg' from your console prompt, see the hardware documentation associated with your system for more information.

To help with your configuration, become familiar with the concepts listed in Table 9-7. See your LAN hardware documentation for configuring information on how to set the jumper settings for those features in Table 9-7.

Table 9-7 ISA Configuration Definitions
Concept Explanation
ISA Slot Number Also called node. The ISA slot number of the device. Writing OpenVMS Alpha Device Drivers in C describes how to number ISA slots.
IRQ Interrupt request line. Used to establish the interrupt level. Boards support IRQs between 1 and 15. Since OpenVMS does not support shared IRQs, every ISA device must have its own IRQ value reserved for it by the console ISACFG utility.
Port Address I/O base control status registers (CSR) address. Boards usually have I/O addresses associated with their CSR locations. These locations must not be used by any other device on the system.
Memory Address Also called shared memory. This address range is used to share memory resident on the adapter card between the host CPU and the LAN device on the adapter card. If the device uses shared memory, the I/O addresses for accessing this memory must be reserved. These locations must not be used by any other device on the system.
DMA Channel If the device performs direct memory access (DMA), either slave or bus mastering, a DMA channel is required. Channels are numbered 1 through 7, but channel 4 is always reserved for the system. See your adapter documentation for DMA channels supported by the device.

9.10.1 OpenVMS LAN Devices Requiring Configuration (Alpha Only)

The DE203, DE204, and DE205 Ethernet and DW110 Token Ring devices require configuration using isacfg. The following information and examples show how this is done.

9.10.1.1 DE203 Ethernet (Alpha Only)

The DE203 is a shared memory Ethernet device. Example 9-1 shows how to configure the OpenVMS software to use the DE203. The following example illustrates a configuration of:

Example 9-1 Using the 'isacfg' at Console Prompt with the DE203 

>>> isacfg -slot 1 -etyp 1 -ena 1 -irq0 5 -iobase0 %x300 
           -membase0 %xd0000 -memlen0 %x1000 -handle "DE20" -mk

The command ("-mk") makes an isacfg entry for an ISA device at slot 1. It is a Single port type of device (-etyp 1). The -handle parameter tells the operating system what type of device it is.

Note
The DE204 and DE205 are variants of the same adapter and are configured in the same way as the DE203.

9.10.1.2 DW110 Token Ring (Alpha Only)

The DW110 is a bus mastering DMA device on the ISA bus. In addition to setting up the ISA I/O parameters, you may configure ring speed (4 or 16 Mbits) and media (UTP or STP). By using LANCP you can also configure ring speed and media during system startup. Example 9-2 shows how to configure the OpenVMS software to use the DW110. The following example illustrates a configuration of:

Example 9-2 Using the 'isacfg' at Console Prompt with the DW110 

>>> isacfg -slot 4 -etyp 1 -ena 1 -irq0 %xa -dmachan0 7 
           -iobase0 %x4e20 -handle "DW11,STP,16" -mk

The command ("-mk") makes an isacfg entry for an ISA device at slot 4. It is a Single port type of device (-etyp 1). The -handle parameter tells the operating system that this is a DW110, that STP media is to be used, and the ring speed is 16.

9.11 Configuring the Ethernet Media Type from the Console (Alpha Only)

On Alpha systems prior to OpenVMS Version 7.1, the SYS$EWDRIVER LAN device driver autosensed the media connection: BNC, AUI, or Twisted Pair. LAN adapters supported by this driver include the DE435, DE450, DE500, and Tulip integral Ethernet device. Their device name under OpenVMS is EWx0, where x is the controller letter.

With OpenVMS Version 7.1, this driver uses the setting of a console environment variable to select the proper media connection. For each EW device recognized by the console there is a console environment variable called EWx0_MODE, where x is the controller letter (e.g. A, B, C). The console environment variable is set with the command: 


>>>SET EWx0_MODE media_selection

In the previous command, the media_selection is one of the following:

During the OpenVMS device configuration a message is sent to the operator's console that shows which media was set by the console and handed to the device driver. For example, if the EWA0_MODE console environment variable was set to Fast the following message would be broadcast at the console: 


  %EWA0, Fast(100baseT) mode set by console

If a console environment variable has been set with an unsupported media type for the corresponding device, then the driver attempts to autosense or auto negotiate the media type. Auto negotiation is supported by the DE500-AA.

An Alpha system console may assign a controller letter to an adapter differently from OpenVMS. In this case, the letter designation in the message broadcast to the console by the driver may not agree with the console setting.

9.12 Frame Formats

Several different LAN physical layer protocols are supported by OpenVMS with some differences in frame formats. The following sections describe the similarities and differences in these frame formats. Despite differences, the QIO interface to the LAN drivers is designed to allow applications to run over the different media with few changes to the application.

The frame formats available in the LAN media are shown in Figure 9-3.

Figure 9-3 LAN Frame Formats

Note that CSMA/CD provides two frame formats and the FDDI provides one frame format. The 802.1 header is an optional extension to the 802.2 header.

9.12.1 CSMA/CD Frames

There are two headers for CSMA/CD frames.

Figure 9-4 illustrates a CSMA/CD frame with an Ethernet header.

Figure 9-4 CSMA/CD Frame with Ethernet Header

The Ethernet header consists of the DA, SA, and PTY fields. Ethernet frames must be at least 64 bytes in length, which means that the minimum data length is 46 bytes. Applications select Ethernet format by specifying NMA$C_LINFM_ETH (the default) as the value for NMA$C_PCLI_FMT in their P2 characteristics buffer. If the amount of actual data to be transmitted is less than 46 bytes, the CSMA/CD drivers transmit extra bytes of zero after the application data.

Figure 9-5 illustrates a CSMA/CD frame with an IEEE 802.3 header.

Figure 9-5 CSMA/CD Frame with IEEE 802.3 Header

The IEEE 802.3 format is similar to the Ethernet format, except the PTY field is replaced by the LEN field.

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