GarrettCom 8000X - Manual (Page 45)

Magnum 8000X Mixed-Media Fiber Hubs Installation and User Guide (05/ 02)
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1. Address Learning (Address Table Maintenance)
The Magnum 8000X bridge module is a state machine design which has a total
address table capacity of 8K addresses. With a large address table, a Magnum 8000X
can serve the needs of a medium-sized to large network. Table 4.2 shows what filter /
forward action the Magnum 8000X will take in each packet-processing situation, and
when a new node address will be added to the internal Address Table. When a new
node-address packet comes into a port for the first time, then the new source address is
“learned” at the same time that the packet is forwarded. After learning, subsequent
packets from the same node address are routinely processed. The address tables are
flushed periodically to update the network status and to purge any inactive stations from
the tables of both domains.
Figure 4.2 : Filtering vs. Forwarding in Dual Speed 8000X
Packet Source Destination Address Table Filter/Forward
Source Address Address Maintenance Action
10 Mbps Not in table Not in table Add source to table Forward
10 Mbps Not in table In table Add source to table Filter
10 Mbps In table Not in table None Forward
10 Mbps In table In table None Filter
100Mbps Not in table Not in table Add source to table Forward
100Mbps Not in table In table Add source to table Filter
100Mbps In table Not in table None Forward
100Mbps In table In table None Filter
Table 4.2: 8000X Dual-Speed Hub Functionality
2. Throughput Increase
By selectively forwarding packets from each domain to the other domain
based on its switching (bridging) logic, the Magnum 8000X increases the available
bandwidth for the users on both sides of the network. As shown in Figure 4.2, it keeps
the local traffic on each side contained, preventing unnecessary packets and bad packets
from traveling to the other domain and using up bandwidth needlessly over there. This
Bridge Module
100 Mb Traffic
100Mb Domain : 100Mb packets are
filtered when the destination address is
in the 100Mb domain address table.
100Mb Domain : 100Mb packets are
forwarded when the destination address is
NOT in the 100Mb domain address table.
10 Mb Domain 100 Mb Domain
10Mb Domain : 10Mb packets are
forwarded when the destination addresse is
NOT in the 10Mb domain address table.
10Mb Domain : 10Mb packets are
filtered when the destination address is
in the 10Mb domain address table.
10 Mb Traffic
10 BUS 100
10 BUS 100