/DECNET /NODECNET Directs LAT protocol to use the DECnet data link address ( /DECNET) or the hardware address (/NODECNET) when starting the LAN controller. If you do not specify the /DECNET or /NODECNET qualifier, the default is that the LAT protocol will use the DECnet data link address. Note that if you enter the CREATE LINK command with the /DECNET qualifier and receive an error message indicating a "bad parameter value," it means the SCSSYSTEMID system parameter is set to an illegal value. To change the value of this parameter, use the following formula: (1024 * a) + n In the formula, a is the DECnet area and n is the DECnet computer number. If the value is outside the range of 1025 to 65535, the LAT protocol cannot start. When you use the /NODECNET qualifier, the LAN device driver code determines which address to use. For example: o If SCSSYSTEMID is set to 0 but DECnet is already running on an Ethernet controller, the LAN device code allows LAT to use the same address as DECnet (AA-00-04-00-xx-xx). o If SCSSYSTEMID is set to 0 and DECnet is not running, the 08- 00-2B-xx-xx-xx address is used (a different address format is used depending on the vendor of your LAN controller). o If the setting for SCSSYSTEMID is the same as the DECnet node number and DECnet is not running, the LAN device code forces LAT to use the AA-00-04-00-xx-xx address. If DECnet is configured on the system (or if the system is part of a cluster), SCSSYSTEMID may contain a nonzero value. This is a problem only when the system has 2 or more LAN controllers connected to the same logical LAN. For example, if your system has an FDDI controller and an Ethernet controller, your site may be configured so that the FDDI ring attached to the FDDI controller and the Ethernet segment attached to the Ethernet controller are bridged by a 10/100 LAN bridge (FDDI-to-Ethernet). In this configuration, it is impossible to run LAT over both controllers. In such a configuration, you must run LAT and DECnet over the same controller if SCSSYSTEMID is not 0. If you fail to do so, DECnet starts first, which in turn causes the LAT startup on the other controller to fail. This failure occurs because LAT startup tries to use the AA-00-04-00-xx-xx address (the DECnet LAN address) but is prevented from doing so by the data link layer. The LAT startup fails because DECnet is already using this address on a different controller. (In a single logical LAN, all data link addresses must be unique. In this setup, both controllers try to use the same address, which is then not unique.) The following command (which creates the LAT link) also fails because the LAN driver tries to use the address based on SCSSYSTEMID: LATCP> CREATE LINK LAT$LINK_2 /NODECNET If SCSSYSTEMID is set to 0, configuring LAT and DECnet on different controllers is possible. However, in a cluster environment, SCSSYSTEMID cannot be set to 0.