We recently ran into a situation where we upgraded a WAN connection from a T1 circuit to a 5mb Ethernet circuit at one of our sites. As soon as we started using the new circuit, we started seeing input overrun errors on the LAN connection to the router from the switch. The uplink was 1 Gb/full duplex. The overrun errors seemed to be caused by too much traffic coming from the LAN side for the router to process out the 5 Mb WAN interface. We set the uplink speed to 100 mb/full duplex and it solved the issue. Is this normal for this type of a WAN connection? How come we didn't have the same issue when using the T1 circuit which is 1.5 Mb? Is there some difference between the way a serial interface and Ethernet interface handle traffic??? The router model is a 2901. Any input would be appreciated.