When running offline test using ethtool -t <eth?> offline:
Link speed falls to 10mb/half duplex. It takes up to 30 seconds before the NIC detects link again.

Use "ethtool -s <nic in test> autoneg on" to force the driver to sync to the 100mb/full duplex speed of the switch and instantly recover link.

This applies to:

Intel® PRO/100 M Desktop Adapter Intel® PRO/100 S Desktop Adapter Intel® PRO/100 S Dual Port Server Adapter Intel® PRO/100 S Management Adapter Intel® PRO/100 S Server Adapter Intel® PRO/100 VE Desktop Adapter Intel® PRO/100 VM Network Connection Intel® PRO/100+ Adapter Intel® PRO/100+ Dual Port Server Adapter Intel® PRO/100+ Management Adapter Intel® PRO/100+ Server Adapter