When an Intel Pro/1000 T NIC is connected to a Catalyst switch, the customer may see poor network connections or excessive numbers of dropped packets. The problem arises when a module with a TBI interface transmits an odd byte packet to a receiver with a Gigabit Media Independent Interface (GMII).
The interoperability issue is a result of the implementation of Carrier Extension. Carrier Extension is detailed in sub section 35.2.3.5 in the IEEE 802.3 specification. Carrier Extension can be used to pad the last byte of a packet, so the packet is aligned on an even numbered boundary.