D-Link xStack DGS-3420 Series Reference Manual page 106

xStack® DGS-3420 Series Layer 2 Managed Stackable Gigabit Switch Web UI Reference Guide
4-37 Example of Port Trunk Group
The Switch treats all ports in a trunk group as a single port. Data transmitted to a specific host (destination address)
will always be transmitted over the same port in a trunk group. This allows packets in a data stream to arrive in the
same order they were sent.
Link aggregation allows several ports to be grouped together and to act as a single link. This gives a bandwidth
that is a multiple of a single link's bandwidth.
Link aggregation is most commonly used to link a bandwidth intensive network device or devices, such as a server,
to the backbone of a network.
The Switch allows the creation of up to 32 link aggregation groups, each group consisting of 2 to 8 links (ports).
Each port can only belong to a single link aggregation group.
All of the ports in the group must be members of the same VLAN, and their STP status, static multicast, traffic
control; traffic segmentation and 802.1p default priority configurations must be identical. Port locking and 802.1X
must not be enabled on the trunk group. Further, the LACP aggregated links must all be of the same speed and
should be configured as full duplex.
The Master Port of the group is to be configured by the user, and all configuration options, including the VLAN
configuration that can be applied to the Master Port, are applied to the entire link aggregation group.
Load balancing is automatically applied to the ports in the aggregated group, and a link failure within the group
causes the network traffic to be directed to the remaining links in the group.
The Spanning Tree Protocol will treat a link aggregation group as a single link, on the switch level. On the port level,
the STP will use the port parameters of the Master Port in the calculation of port cost and in determining the state
of the link aggregation group. If two redundant link aggregation groups are configured on the Switch, STP will block
one entire group; in the same way STP will block a single port that has a redundant link.
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