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 HP OpenVMS I/O User's Reference Manual |
 Local Area Network (LAN) Device Drivers |
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Format of Ethernet Addresses
An Ethernet address is 48 bits in length. Ethernet addressesare represented by the Ethernet standard as six pairs of hexadecimaldigits (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 whichthey are transmitted; bits within each byte are transmitted fromright to left. In this example, byte AA is transmitted first; byteFF is transmitted last. (See the description of NMA$C_PCLI_PHA in P2 Attributes, Set Controller Mode, for the internal representationof addresses.)
Upon application, IEEE assigns a block of addresses to a producerof LAN nodes. Thus, every manufacturer has a unique set of addressesto use. Normally, one address out of the assigned block of physicaladdresses is permanently associated with each controller (usuallyin read-only memory). This address is known as the hardware addressof the controller. Each individual controller has a unique hardwareaddress.
Ethernet Address Classifications
An Ethernet address canbe a physical address of a single node or a multicast address, dependingon the value of the low-order bit of the first byte of the address(this bit is transmitted first). Following are the two types of nodeaddresses:
Contrary to the Ethernet specification and the IEEE 802.3Standard, the broadcast address (FF-FF-FF-FF-FF-FF) must be enabledas a multicast address to receive messages addressed to it.
Selecting an Ethernet Physical Address
The OpenVMS interface to the LAN controllers allows you toset a physical address of the controller. The selection of the physicaladdress of a LAN controller is different for CSMA/CD (Ethernet and802.3) and FDDI.
For CSMA/CD, all users of the controller must agree on thisaddress. The first user of the controller chooses the physical address;any additional users of the controller must specify either the samephysical address, no physical address, or change the address (ifallowed). When all channels to the controller are shut down, the nextuser to start a channel chooses the physical address. The controller'sphysical address is always chosen on the first successful startupwhen there are no active ports. If the address is not chosen atthis time, the controller's hardware address is used as the physicaladdress.
For CSMA/CD, the Can Change Address parameter allows the physicaladdress to be changed even though there are active users. If allcurrent users of the controller have set the NMA$C_PCLI_CCA parameterto NMA$C_STATE_ON, then the physical address can be changed.
For FDDI, each port using a controller may specify its ownunique physical address. Any combination of sharing of physicaladdresses is also allowed across the ports of an FDDI controller.For example, ports A, B, and C may use one unique physical addressand ports D and E may use another unique address.
Ethernet Physical and Multicast Address Values
The following shows the multicast addresses assigned for usein cross-company communications:.
| Value | Meaning |
|---|---|
| FF-FF-FF-FF-FF-FF | Broadcast |
| CF-00-00-00-00-00 | Loopback assistance |
The following lists the 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 HP customersfor 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 |
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 LANaddress mechanism. Instead, it uses functional addresses.These functional addresses are locally administered group addresses(multicast addresses). The first two bytes of the address are always03-00 (canonical format), and the remaining four bytes contain abit mask that specifies which of the 32 possible combination masksis being described.
Because most OpenVMS LAN applications use standard multicastaddresses, a mechanism has been designed to map functional addressesto globally and locally administered multicast addresses. This allows applicationsto use the same multicast addresses that are used in the other LANmedia.
Address Mappings of Token Ring Drivers shows thedefault mapping used by the OpenVMS Alpha Token Ring drivers:
If an application needs to change or add mappings, QIOs existfor performing such operations. If the system or network managerhas a requirement regarding mapping of the functional addresses,the LAN control program (LANCP) utility may be used to manage themapping. The following example maps the multicast address AB-01-01-01-02-03to functional address 03-00-00-01-00-00 on Token Ring device ICA0:.
$ MCR LANCPLANCP>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 addressto map to the same functional address. In all cases, the use ofthe functional address is associated with an individual application'sprotocol.
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