All SFP modules contain in their EEPROM, a Serial Number, Vendor Name & ID, Security code and a CRC. The Switch checks this information, if it can’t verify it might give messages like the following:
strong>%PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported transceiver found in Gi1/0/1
%GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port 65538 has bad crc

There are two undocumented cisco commands to get 3rd party SFP modules to work:
strong>switch(config)# service unsupported-transceiver
switch(config)# no errdisable detect cause gbic-invalid

So should you use non Cisco SFPs? What’s the difference anyway? This has come up recently. Whilst some are to be avoided, such as those maybe from China, which are in fact Cisco replica’s, some (which can even be coded to meet Cisco requirements apparently) perform well, with no less performance than the genuine Cisco part. Now, whether Cisco will be happy about this is another story. Interesting command to note though just in case.