Technical data

Fabric OS Administrator’s Guide 12-3
Publication Number: 53-0000518-09
Fabric Considerations
12
• SilkWorm 3016: Trunks are supported on the two external ports (0 and 15).
Fabric Considerations
The ISL Trunking feature is provided with the Fabric OS and can be activated by entering a license key,
available from the switch supplier. When the ISL Trunking license is activated (after you have entered
the switchDisable and switchEnable commands), trunking is automatically implemented for any
eligible ISLs.
A license must be activated on each switch that participates in trunking. For the SilkWorm 12000, a
single license key enables the feature on both logical switches.
To use ISL Trunking in the fabric, the fabric must be designed to allow trunking groups to form. To
identify the most useful trunking groups, evaluate the traffic patterns before designing or redesigning
the fabric. This also applies to the Silkworm 24000 configured with two domains, and the SilkWorm
48000, which does not support two domains.
ISL Trunking can be used to simplify storage area network design and improve performance. When
designing the SAN, consider the following recommendations in addition to the standard guidelines for
SAN design:
• Evaluate the traffic patterns within the fabric.
• Place trunking-capable switches adjacent to each other.
This maximizes the number of trunking groups that can form. If you are using a core/edge
topology, place trunking-capable switches at the core of the fabric and any switches that are not
trunking-capable at the edge of the fabric.
• Activate an ISL Trunking license on each switch that is to participate in a trunking group.
• Cable lengths for participating links should differ by no more than 550 meters.
• When connecting two switches with two or more ISLs, ensure that all trunking requirements are
met to allow a trunking group to form.
• Determine the optimal number of trunking groups between each set of linked switches, depending
on traffic patterns and port availability.
The goal is to avoid traffic congestion without unnecessarily using ports that could be used to
attach other switches or devices. Consider these points:
- Each physical ISL uses two ports that could otherwise be used to attach node devices or other
switches.
- Trunking groups can be used to resolve ISL oversubscription if the total capability of the
trunking group is not exceeded.
• Consider how the addition of a new path will affect existing traffic patterns:
- A trunking group has the same link cost as the master ISL of the group, regardless of the
number of ISLs in the group. This allows slave ISLs to be added or removed without causing
data to be rerouted, because the link cost remains constant.
- The addition of a path that is shorter than existing paths causes traffic to be rerouted through
that path.
- The addition of a path that is longer than existing paths might not be useful because the traffic
will choose the shorter paths first.
• Plan for future bandwidth addition to accommodate increased traffic.