We have a Cisco 2801 plugged in to a CAT2950 switch. The router IOS is c2801-advipservicesk9-mz.124-8c.bin and the switch IOS is c2950-i6q4l2-mz.121-22.EA9.bin.
When the devices are reset/reloaded the state of the link between the devices comes up but CRC errors are shown on the switch port and there is 80-90% packet loss.
If a different switch port is used the problem still occurs. The router interface is fastethernet0/1 and the switch interface is fastethernet0/3.
The only way to stop the errors is to manually shutdown and then open the interfaces.
description **** Trunk link to router FastEthernet0/1 ****
switchport trunk allowed vlan X,X,X
switchport mode trunk
description Trunk to Switch FastEthernet 0/3
no ip address
no ip route-cache cef
no ip route-cache
no ip split-horizon