Allied Telesis AT-S25 - Manual (Page 72)

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The ports of a port trunk must be members of the same group. You
cannot use ports from different groups. For example, you could use
ports 4 and 5 on an AT-8324 switch as one port trunk, since the ports are
members of the same group. However, ports 7, 8, 9, and 10 cannot be
combined to form a port trunk on an AT-8324 switch because they
belong to different groups.
Guideline 4: Creating Only One Trunk Per Group
Each group of ports on an Ethernet switch can support only one port
trunk. For example, the AT-8324 Ethernet switch has three port groups,
assuming no expansion modules have been installed in the switch.
Consequently, this switch can support three port trunks, one port trunk
for each port group. The addition of two expansion modules would
enable the switch to support two additional port trunks, one for each
module.
Guideline 5: Using Consecutive Ports
The ports of a trunk must be consecutive. For example, you could use
ports 4, 5, 6, and 7 as one port trunk, because the ports are consecutive.
Guideline 6: Cabling Based on Port Number
When cabling a trunk, it is important that the order of the connections
be identical on both nodes. The lowest numbered port in a trunk must
be connected to the lowest numbered port of the trunk on the other
device, the next lowest numbered port must be connected to the next
lowest numbered port on the other device, and so on.
For example, assume that you are connecting a trunk between two
AT-8324 switches. On the first AT-8324 switch you had chosen ports 12,
13, 14, 15 from port group two for the trunk. On the second AT-8324
switch you had chosen ports 21, 22, 23, and 24 from port group 3. To
maintain the order of the port connections, you connect port 12 on the
first AT-8324 switch to port 21 on the second AT-8324, port 13 to port 22,
and so on.
Guideline 7: Configuring the Port Parameters of a Port Trunk
The ports in a trunk automatically assume the same configuration (such
as VLAN membership) as the configuration of the lowest numbered port.
For example, if you create a trunk consisting of ports 4, 5, 6, and 7, port 4
is the master port and its configuration is propagated to ports 5, 6, and 7.
As long as the ports are configured as a trunk, you must not change any
of the attributes of ports 5, 6, and 7 that might conflict with the settings
of port 4.