The IEEE 802.3u specification requires that all external MII transceivers are configured to respond to PHY address zero. Fast Ethernet MII transceivers shipped from Allied Telesyn prior to January 1, 1998 are configured with PHY address one selected.
For Cisco products running Cisco IOS version 11.1(14.5)CA and later, the Fast Ethernet interface will see the following symptoms:
Fast Ethernet Mode
For half-duplex Fast Ethernet interfaces with a misconfigured MII transceiver, the port will toggle between line up and line down states.
For full-duplex Fast Ethernet interfaces with a misconfigured MII transceiver, the port will remain in the line down state.
Workaround - Updated Jan. 6, 1998
A temporary workaround for the line flapping problem is to disable keepalives (on by default) on the Fast Ethernet port, until the transceiver is replaced. Please remember to re-enable the keepalives again after replacing the transceiver, since the interface will not be able to detect line down until keepalives are re-enabled.
MII transceivers that have user-configurable address settings (dip-switches), such as the following Allied Telesyn model numbers can be set to PHY address zero:
For MII transceivers that are preconfigured for PHY address one and do not have user-configurable address settings, customers must contact the vendors directly to arrange for replacements.
Identifying Problem Transceivers
Suspect MII transceivers can easily be electronically identified using the Cisco global commands show cont vip <#> tech for the Cisco 7000 and Cisco 7500 series products and show cont fastether <#> for the Cisco 7200 series. After entering the respective show cont command, look for the "MII Registers:" section as follows:
The router output when an MII transceiver configured for PHY address zero:
If all values displayed are "0xFFFF" as in the example above, then the MII transceiver is either non-compliant (PHY address one) or it is defective. If the transceiver is configured for PHY address zero and the router still displays "0xFFFF", then the transceiver is defective and the manufacturer should be contacted to arrange for a replacement.
For More Information
If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods: