switchport trunk allowed - Cisco / HP

[Harv Cee]

Hi, I have a simple query and just seeking some clarification....

I have a Cisco 3750X with various vlans configured. One interface has the command: "Switchport Trunk allowed vlan 100, 200". I understand it will ONLY forward packets for vlan 100 & 200 on this interface - certainly the case if connected to another Cisco device.

On the other end of the interface is a HP1810 switch. The ports are configured for vlan 100, 200 and 300. I have looked at the config of the Cisco stack and there is no mention of vlan 300 at all. Is it safe to assume the Cisco switch is not doing any forwarding for vlan 300 to the HP if it is not defined in its config or the allowed command?

Thanks, Harv

[manish arora · Accepted solution]

yes, you can assume that the Cisco switch is not forwarding anything from itself to towards HP for vlan 300 but the HP will be sending the traffic for VLAN300 on the Tagged ports. 

I think you can remove the Tagged PORTNAME on HP under the VLAN 300 configuration as well. Removing the Tagged PortXX under the vlan 300 configuration on HP where XX is the trunk port connecting to the Cisco will stop HP for forwarding any traffic towards the Cisco as well.

Manish