The flow control settings must match on both sides for the link to come up. It is highly recommended that you configure auto-negotiation to on for both devices. (Auto-negotiation is enabled by default on all Catalyst switches.) Otherwise, if you have a layer 1 problem, the link remains up and a unidirectional link will result.
The initial software releases that support Gigabit Ethernet on the GSR router do not support gigabit auto-negotiation.
The following command configures gigabit auto-negotiation on the Catalyst 6000/6500:
set port negotiation module/port disable|enable