Link Aggregation Concepts; Rules And Limitations - Siemens RUGGEDCOM ROS User Manual

Chapter 5
Setup and Configuration
ROS allows up to 15 port trunks to be configured on a single device, with each consisting of up to 8 ports.
NOTE
The maximum number of port trunks for each device depends on the number of ports available. At
least two ports are required to configure a port trunk.
NOTE
The aggregated port with the lowest port number is called the Port Trunk Primary Port. Other ports in
the trunk are called Secondary Ports.
The following sections describe how to configure and manage link aggregation:
• Section 5.11.1, "Link Aggregation Concepts"
• Section 5.11.2, "Managing Port Trunks"
Section 5.11.1

Link Aggregation Concepts

The following sections describe some of the concepts important to the implementation of link aggregation in ROS:
• Section 5.11.1.1, "Rules and Limitations"
• Section 5.11.1.2, "Link Aggregation and Layer 2 Features"
• Section 5.11.1.3, "Link Aggregation and Physical Layer Features"
Section 5.11.1.1

Rules and Limitations

The implementation of link aggregation must adhere to the following rules and limitations:
• Each port can belong to only one port trunk at a time.
• A port mirroring target port can not be member of a port trunk. However, a port mirroring source port can be
member of a port trunk.
• A port working in QinQ mode cannot be a member of a port trunk.
• DHCP Relay Agent Client port cannot be a member of a port trunk.
• Load balancing between the links of a bundle is randomized and may not be ideal. For instance, if three 100
Mbs links are aggregated, the resulting bandwidth of the port trunk may not be precisely 300 Mbs.
• A Static MAC Address should not be configured to reside on an aggregated port – it may cause some frames
destined for that address to be dropped.
• A secure port cannot be a member of a port trunk.
• The IEEE 802.3ad Link Aggregation standard requires all physical links in the port trunk to run at the same
speed and in full-duplex mode. If this requirement is violated, the performance of the port trunk will drop.
The switch will raise an appropriate alarm, if such a speed/duplex mismatch is detected.
• STP dynamically calculates the path cost of the port trunk based on its aggregated bandwidth. However, if the
aggregated ports are running at different speeds, the path cost may not be calculated correctly.
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RUGGEDCOM ROS
User Guide
Link Aggregation Concepts