Trunk wont allow vlans

[SandervdA]

Hello,

I'm trying to create a trunk on a Cicso C2960X switch on port 1/0/48. in the 'sh int status' it says that port 1/0/48 is a trunk. but when i type 'sh int gi1/0/48 trunk it shows that there are not vlan allowed on the trunk:

 To add a vlan to the trunk I type:

-conf

-int gi1//0/48

-switchport mode trunk

-switchport trunk allowed vlan 1, 117, 126

-end

-wr

configuration switches and netwerking is all fairly new to me, and i dont know why its not working.

[MHM Cisco World]

If I am right 3com with SW 

mismatch speed/duplex 

you need manual config of speed and duplex on both SW to UP the port.

[rasmus.elmholt]

The speed and duplex is configured as Auto.

A switch configured with speed auto will automatically sense the speed at the other end if it is statically configured.

Duplex should negotiate to half if the other end is configured staticaly.

None of this can explain the issues we see here. IMHO.

[MHM Cisco World]

https://iztg.com/issue-on-cisco-gige-port-with-3com-switches/

read this doc.

this is why I suspect the speed duplex mismatch. 
use manual not auto and check

[paul driver]

Hello

@MHM Cisco World  It shouldnt matter what speed/duplex setting is appended to a interface or if the other end of the trunk isn't configured. As long as the switchport interface that is to be a trunk is enabled as a trunk it should at the very least show vlans that are active and allowed to cross the trunk.