No uplink on 3750 switch

[BHconsultants88]

Hi everyone

I'm having a few problems getting the uplink port on a 3750 to stay up. The port on the router it's connected to keeps going into error disabled mode. Could someone take a look at the switch config and let me know if it looks ok? Uplink port on the switch is port 48.

Thanks

[Julio E. Moisa]

Hi

have you configured native vlan on the sub-interface on the router? Your config on the switch is ok.

Vlan 58
name native-vlan

interface FastEthernet8/0/48
switchport trunk encapsulation dot1q
switchport trunk native vlan 58
switchport mode trunk

Router example config

inteface Fx/x.58
encapsulation dot1q 58 native

Now, shutdown and not shutdown the trunk and verify again. 

Note: the native vlan should not be used for other role than native, in few words it should not be configured for access ports.

Hope it is useful

:-)

[Georg Pauwen]

Hello,

in addition to Julio's post, you also might want to try and/or:

interface FastEthernet8/0/48
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 58
 switchport mode trunk
 switchport nonegotiate
 spanning-tree portfast trunk