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How can I see what VLANs are allowed?
Use the show interfaces trunk command to check whether the local and peer native VLANs match. If the native VLAN does not match on both sides, VLAN leaking occurs. Use the show interfaces trunk command to check whether a trunk has been established between switches.
What is Switchport trunk allowed?
The switchport trunk allowed vlan command is used to specify the list of VLANs that are allowed on a trunk port. When a Layer 2 interface on a Cisco IOS device is configured to operate in trunk mode, the default setting is for the interface to carry all of the VLANs defined on the switch.
How to configure allowed VLANs on trunk?
Configure allowed VLANs on trunk. By default, all VLANs are allowed across the trunk link. We can verify that using the show interfaces trunk command: You can prevent traffic from certain VLANs from traversing a trunked link using the following interface mode command: switchport trunk allowed vlan {add | all | except | remove} vlan-list.
When to use VTP pruining to block VLANs?
VTP Pruining will not restrict VLAN traffic from a trunk, it will merely “Prune” it when it is not required. The switchport trunk allowed vlan command should be used to actually block VLANs from going over the trunk. (Make sure its the same at both ends otherwise you’ll end up with lots of discards…)
Can a VLAN be connected to a tunnel port?
Dynamic Trunking Protocol (DTP) is not supported on tunnel ports. A trunk is a point-to-point link between one or more Ethernet switch interfaces and another networking device such as a router or a switch. Ethernet trunks carry the traffic of multiple VLANs over a single link, and you can extend the VLANs across an entire network.
Which is the default VLAN on a Cisco switch?
VLAN 1 is the default VLAN on all trunk ports in all Cisco switches, and it has previously been a requirement that VLAN 1 always be enabled on every trunk link.