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Advanced POWER Virtualization on IBM System p5 - Previous ...

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2. Tagged port receives a packet tagged with the PVID or <strong>on</strong>e of the assigned<br />

VIDs:<br />

The packet will be forwarded without modificati<strong>on</strong>.<br />

3. Tagged port receives a packet tagged with any VLAN ID other than the PVID<br />

or assigned additi<strong>on</strong>al VIDs:<br />

The packet will be discarded.<br />

Thus, a tagged port will <strong>on</strong>ly accept untagged packets and packets with a VLAN<br />

ID (PVID or additi<strong>on</strong>al VIDs) tag of these VLANs that the port has been assigned<br />

to. The sec<strong>on</strong>d case is the most typical.<br />

Receiving packets <strong>on</strong> an untagged port<br />

A switch port c<strong>on</strong>figured in the untagged mode is <strong>on</strong>ly allowed to have a PVID<br />

and will receive untagged packets or packets tagged with the PVID. The<br />

untagged port feature helps systems that do not understand VLAN tagging<br />

(VLAN unaware hosts) to communicate with other systems using standard<br />

Ethernet.<br />

An untagged port uses the following rules when receiving a packet from a host:<br />

1. Untagged port receives an untagged packet:<br />

The packet is tagged with the PVID, then forwarded.<br />

2. Untagged port receives a packet tagged with the PVID:<br />

The packet is forwarded without modificati<strong>on</strong>.<br />

3. Untagged port receives a packet tagged with any VLAN ID other than the<br />

PVID:<br />

The packet is discarded.<br />

The first case is the most typical; the other two should not occur in a properly<br />

c<strong>on</strong>figured system.<br />

After having successfully received a packet over a tagged or untagged port, the<br />

switch internally does not need to handle untagged packets any more, just<br />

tagged packets. This is the reas<strong>on</strong> why multiple VLANs can easily share <strong>on</strong>e<br />

physical uplink to a neighbor switch. The physical uplink is being made through<br />

trunk ports that have all the appropriate VLANs assigned.<br />

76 <str<strong>on</strong>g>Advanced</str<strong>on</strong>g> <str<strong>on</strong>g>POWER</str<strong>on</strong>g> <str<strong>on</strong>g>Virtualizati<strong>on</strong></str<strong>on</strong>g> <strong>on</strong> <strong>IBM</strong> <strong>System</strong> <strong>p5</strong>

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