300-170, Cisco Exams

Shut down or not shut down – Cisco Unified Computing Systems Overview

When you delete a specified VLAN, the ports associated with that VLAN are shut down and no traffic flows. However, the system retains all of the VLAN-to-port mappings for that VLAN. When you re-enable or re-create the specified VLAN, the system automatically reinstates all of the original ports to that VLAN.

If a VLAN group is used on a vNIC and also on a port channel assigned to an uplink, you cannot delete and add VLANs in the same transaction. The act of deleting and adding VLANs in the same transaction causes ENM pinning failure on the vNIC. vNIC configurations are done first, so the VLAN is deleted from the vNIC and a new VLAN is added, but this VLAN is not yet configured on the uplink. Hence, the transaction causes a pinning failure. You must add and delete a VLAN from a VLAN group in separate transactions.

Access ports only send untagged frames and belong to and carry the traffic of only one VLAN. Traffic is received and sent in native formats with no VLAN tagging. Anything arriving on an access port is assumed to belong to the VLAN assigned to the port.

You can configure a port in access mode and specify the VLAN to carry the traffic for that interface. If you do not configure the VLAN for a port in access mode or an access port, the interface carries the traffic for the default VLAN, which is VLAN 1.

You can change the access port membership in a VLAN by configuring it. You must create the VLAN before you can assign it as an access VLAN for an access port. If you change the access VLAN on an access port to a VLAN that is not yet created, the Cisco UCS Manager shuts down that access port.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address. If you assign an access VLAN that is also a primary VLAN for a private VLAN, all access ports with that access VLAN receive all the broadcast traffic for the primary VLAN in the private VLAN mode.

Trunk ports allow multiple VLANs to transport between switches over that trunk link. A trunk port can carry untagged packets simultaneously with the 802.1Q tagged packets. When you assign a default port VLAN ID to the trunk port, all untagged traffic travels on the default port VLAN ID for the trunk port, and all untagged traffic is assumed to belong to this VLAN. This VLAN is referred to as the native VLAN ID for a trunk port. The native VLAN ID is the VLAN that carries untagged traffic on trunk ports.

The trunk port sends an egressing packet with a VLAN that is equal to the default port VLAN ID as untagged; all the other egressing packets are tagged by the trunk port. If you do not configure a native VLAN ID, the trunk port uses the default VLAN.

Note

Changing the native VLAN on a trunk port or an access VLAN of an access port flaps the switch interface.

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