As a worst case example, if it takes 60 seconds for each of the recommended 200
stations to transmit a message, it could take 200 minutes to complete the address
database annotations. However, the DECbridge 90 unit tries to expedite the
transmission as follows:
•
If the station remains quiet after waiting 30 seconds for a message, the
DECbridge unit attempts to generate a response using the IEEE XID request.
•
If the IEEE XID request fails, the DECbridge unit tries a MOP system-ID
request.
For these reasons, the DECbridge unit never hangs for more than 30 seconds
on an IEEE conforming station, or for more than 60 seconds on any Digital
station that predates the IEEE specifications. If you are monitoring messages
and protocols on your work group Ethernet, you occasionally see these messages.
Using the WGB Address Table for Work Group
Management
The work group bridge Ethernet address table is dynamic: Ethernet addresses
are added to the table when a device first transmits on the network; addresses
are removed when a device does not retransmit for a user-specified period, from
1 to 32767 seconds (about 10 hours). The default is 15 minutes. When a device
is learned or relearned after it has timed out, the address is listed in the lowest
empty entry of the address table.
This continuous learning, timeout, and relearning of the Ethernet addresses
means that devices in a particular work group may or may not be in the address
table at any moment. If they are in the address table, they may not be in a
consistent database location. Devices such as personal computers or laptop
computers that are removed and reconnected elsewhere, timeout from the address
table. When the device is reconnected, the addresses for these devices are stored
in a different address table location.
Because the address table is dynamic, the network manager cannot easily
compare printouts of the work group bridge address table to determine work
group changes on a day-to-day or week-to-week basis.
Management Details B–3