cp2200 Silicon Laboratories, cp2200 Datasheet - Page 105

• Manufacturer Part Number: cp2200
• Description: Single-chip Ethernet Controller
• Manufacturer: Silicon Laboratories

CP2200/1
17.2. MAC Address Filtering
Problem
For unicast packets received over the Ethernet wire, the receive filter only validates the first 5 bytes of the 6-byte
Ethernet MAC Address. Any packet addressed to a device whose MAC address only differs in the 6th byte will be
allowed to pass through the receive filter.
Workaround
The Ethernet driver on the host controller should verify that the 6th byte of each packet (i.e., the final byte of the
MAC address) matches its assigned MAC address. If it detects a mismatch, the packet should be discarded by
writing 1 to the RXSKIP bit.
Implications on Throughput
This behavior does not slow down the rate which the embedded system can send or receive packets, since the
CP220x must receive and filter all packets on the network. However, it can interrupt the host controller for received
packets addressed to another device with a similar MAC address (where the only difference is in the 6th byte) on
the same subnet. On a managed switch network, present on most corporate LANs, the effect of this behavior is
minimal due to the fact that the managed switch filters out unicast packets not addressed to the receiving Ethernet
device.
Rev. 1.0
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