CP2201 datasheet(105/108 Pages) SILABS

105 / 108 page

CP2200/1

Rev. 1.0

105

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.

CP2201 Datasheet(PDF) 105 Page - Silicon Laboratories