Which vlans will be allowed across the trunk

VLANs 1 through are allowed on each trunk by default. However, VLAN traffic can be removed from the allowed list. This keeps traffic from the VLANs from passing over the trunk link. This parameter is described by two VLAN numbers separated by a hyphen. For example, to remove VLANs 5 through 10 and 12 from the trunk, issue the switchport trunk allowed vlan remove , 12 command.

To add a VLAN to the trunk, issue the switchport trunk allowed vlan add vlan-list command. What is the advantage of allowing certain vlans vs allowing all? Currently we have all vlans allowed in the network and want to allow only certain vlans instead; how can we determine which vlans to be allowed?

If the network administrator can't tell the purpose of the various VLANs you have a secious problem! VLANs are used to have just one backbone but providing "shielded" separate networks within that infrastructure. As an example for allowing only specific VLANs imagine a company that has an ICT department that provides the network backbone and the programmer department is having some ESX servers running.

For the ports in trunk mode this will not help thus you have to check the device attached to the port for its configuration. All in all coming back to the question: why did you allow all VLANs on all trunk ports ultimately resulting in not beeing able to answer the question which device is member of which VLAN.

To restrict the traffic that a trunk carries, issue the switchport trunk allowed vlan vlan-list interface command". Its a very old infrastructure only one copper drop per classroom. The copper directly connects to the Access Point, and the AP has an additional mb port that we connect the phone to.

Clearly this would need to be a trunked port for all the devices to work, but why bombard the port and devices with traffic from every single VLAN in the infrastructure ours has about 30 , when all we need is traffic from the 3 VLANs? I've also heard of Administrators doing this in the backbone of the network for load balancing. Buy or Renew. Find A Community. Cisco Community. Join us in congratulating October's Spotlight Award Winners!

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