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3.13 Trunk
The Port Trunk Configuration is used to configure the settings of Link Aggregation. You can bundle more than
one port with the same speed, full duplex and the same MAC to be a single logical port, thus the logical port
aggregates the bandwidth of these ports. This means you can apply your current Ethernet equipments to build
the bandwidth aggregation. For example, if there are three Fast Ethernet ports aggregated in a logical port,
then this logical port has bandwidth three times as high as a single Fast Ethernet port has.
The switch supports two kinds of port trunk methods:
LACP
Ports using Link Aggregation Control Protocol (according to IEEE 802.3ad specification) as their trunk method
can choose their unique LACP GroupID (1~3) to form a logic “trunked port”. The benefit of using LACP is that
a port makes an agreement with its peer port before it becomes a ready member of a “trunk group” (also called
aggregator). LACP is safer than the other trunk method - static trunk.
The switch LACP does not support the followings:
y
Link Aggregation across switches
y
Aggregation with non-IEEE 802.3 MAC link
y
Operating in half-duplex mode
y
Aggregate the ports with different data rates
Static Trunk
Ports using Static Trunk as their trunk method can choose their unique Static GroupID (also 1~3, this Static
groupID can be the same with another LACP groupID) to form a logic “trunked port”. The benefit of using Static
Trunk method is that a port can immediately become a member of a trunk group without any handshaking with
its peer port. This is also a disadvantage because the peer ports of your static trunk group may not know that
they should be aggregate together to form a “logic trunked port”. Using Static Trunk on both end of a link is
strongly recommended. Please also note that low speed links will stay in “not ready” state when using static
trunk to aggregate with high speed links.
As to system restrictions about the port aggregation function on the switch. In the management point of view,
the switch supports maximum 3 trunk groups for LACP and additional 3 trunk groups for Static Trunk. But in
the system capability view, only 8 “real trunked” groups are supported. An LACP trunk group with more than
one ready member-ports is a “real trunked” group. An LACP trunk group with only one or less than one ready
member-ports is not a “real trunked” group. Any Static trunk group is a “real trunked” group.
Per Trunk Group supports a maximum of 4 ready member-ports. Please note that some decisions will
automatically be made by the system while you are configuring your trunk ports. Some configuration examples
are listed below:
y
Rule1: Maximum 3 groups are allowed
y
Rule 2: The members of each group cannot exceed more than 4 ports
y
Rule 3: Group 1 and 2 cannot exist member 25 and 26 port
y
Rule 4: Group 3 cannot exist member from 1 to 24 port
