Solved: sg300 strange running-config

Mary Poppins · ‎11-07-2014

dear all,

In my sg300 switch I configured the gi port as trunk:

switchport mode trunk

switchport trunk allowed vlan add 1

no spanning-tree portfast

no spanning-tree bpduguard

however the 'trunk allowed vla add 1' line generate error, i think because vlan 1 is the default, when i check the port it shows trunk, and it is operate well.

But wehen i show running-config it shows only this:

interface gigabitethernet1
no spanning-tree portfast

Why is the switchport mode trunk and the trunk allowed commands missing in the running-config? However I have another trunk port with allowed vlan 1,3, that is included partly in the running-config, but there is no switchport mode trunk

interface gigabitethernet52
no spanning-tree portfast
spanning-tree port-priority 16
switchport trunk allowed vlan add 3

Is the trunk the base config, so it is left by default?

thank you

devils_advocate · ‎11-10-2014

Dynamic Desirable is the default.

Effectively the switch will negotiate with whatever the port is plugged into.

If the other side is a Trunk, it will form a Trunk
If the other side is an Access Port, they will both be an access port.

Vlan 1 is the Native and default vlan, therefore is always allowed on the Trunk, hence why it does not show up in the running config.

The running config will only show commands which are not the default.

I suspect whatever port interface gigabitethernet52 is plugged into on the other end, the config will be a Trunk because the default is to negotiate.

View solution in original post