zl50409 Zarlink Semiconductor, zl50409 Datasheet - Page 36

• Manufacturer Part Number: zl50409
• Description: Managed 9-port 10/100m Ethernet Switch
• Manufacturer: Zarlink Semiconductor

If the destination MAC address belongs to a port trunk, then the trunk number is retrieved instead of the port
number. But on which port of the trunk will the frame be transmitted? This is easily computed using a hash of the
source and destination MAC addresses.
When all the information is compiled, the switch response is generated, as stated earlier. The search engine also
interacts with the CPU with regard to learning and aging.
5.3
5.3.1
The search block performs source MAC address and destination MAC address (or destination IP address for IP
multicast) searching. As we indicated earlier, if a match is not found, then the next entry in the linked list must be
examined, and so on until a match is found or the end of the list is reached.
In tag-based VLAN mode, if the frame is unicast, and the frame's destination port is recognized as a member of the
VLAN, then the frame is forwarded to that port; otherwise, the frame is forwarded to all the members in the VLAN
domain. If the frame is multicast or broadcast, the frame is forwarded to all the members in the VLAN. Moreover, if
port trunking is enabled, this block selects the destination port (among those in the trunk group).
In port based VLAN mode, a bit map is used to determine whether the frame should be forwarded to the outgoing
port. The main difference in this mode is that the bit map is not dynamic. Ports cannot enter and exit groups
because of real-time learning made by a CPU.
The MAC search block is also responsible for updating the source MAC address timestamp used for aging.
5.3.2
The learning module learns new MAC addresses and performs port change operations on the MCT database. The
goal of learning is to update this database as the networking environment changes over time.
When CPU reporting is enabled, learning and port change will be performed when the CPU request queue has
room, and a “Learn MAC Address” message is sent to the CPU.
5.3.3
Aging time is controlled by register 400h and 401h.
The aging module scans and ages MCT entries based on a programmable “age out” time interval. As we indicated
earlier, the search module updates the source MAC address timestamps for each frame it processes. When an
entry is ready to be aged, the entry is removed from the table, and a “Delete MAC Address” message is sent to
inform the CPU.
Supported MAC entry types are: dynamic, static, source filter, destination filter, IP multicast, source and destination
filter, secure and multicast MAC address. Only dynamic entries can be aged; all others are static. The MAC entry
type is stored in the “status” field of the MCT data structure.
5.4
The ZL50409's implementation of intelligent traffic switching provides filters for source and destination MAC
addresses. This feature filters unnecessary traffic, thereby providing intelligent control over traffic flows and
broadcast traffic.
Broadcast, unknown unicast or unknown multicast MAC address can also be filter on per VLAN basis.
MAC address filtering allows the ZL50409 to block an incoming packet to an interface when it sees a specified MAC
address in either the source address or destination address of the incoming packet. For example, if your network is
congested because of high utilization from a MAC address, you can filter all traffic transmitted from that address
and restore network flow, while you troubleshoot the problem.
Search, Learning, and Aging
MAC Address Filtering
MAC Search
Learning
Aging
Zarlink Semiconductor Inc.
ZL50409
36
Data Sheet