GarrettCom Address Learning Address Table Maintenance, 8000X Dual-Speed Hub Functionality

Magnum 8000X Mixed-Media Fiber Hubs Installation and User Guide (05/ 02)

1.Address Learning (Address Table Maintenance)

10Mb Domain : 10Mb packets are					100Mb Domain : 100Mb packets are
forwardedwhen the destination addresse is
NOTin the 10Mb domain address table.					forwardedwhen the destination address is
					NOTin the 100Mb domain address table.
10Mb Domain : 10Mb packets are	10		BUS	100
filteredwhen the destination address is
in the 10Mb domain address table.	Bridge Module
10 Mb Domain					100 Mb Domain
		10	BUS	100
10 Mb Traffic					100 Mb Traffic
					100Mb Domain : 100Mb packets are
					filteredwhen the destination address is
					in the 100Mb domain address table.

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

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