ProLiant BL p-Class GbE2 Interconnect Switch Application Guide

Ports and trunking 31
Table 6 Ethernet switch port names
Port number LED Port alias
21 P21 Uplink3
22 P22 Uplink4
23 P23 FrontPanel1
24 P24 FrontPanel2
Port trunk groups
When using port trunk groups between two GbE2 Interconnect Switches, you can create an aggregate link
operating at up to four Gigabits per second, depending on how many physical ports are combined. The GbE2
Interconnect Switch supports up to 12 trunk groups per switch, each with up to six ports per trunk group.
The trunking software detects mis-configured (or broken) trunk links and redirects traffic on the mis-configured or
broken trunk link to other trunk members within that trunk. You can only use trunking if each link has the same
configuration for speed, flow control, and auto-negotiation.
Statistical load distribution
In a configured trunk group containing more than one port, the load distribution is determined by information
embedded within the data frame. For broadcast, multicast traffic, and unknown unicast packets, the lowest port
number in the trunk group is elected to be the port for forwarding traffic. For IP traffic, the GbE2 Interconnect
Switch will calculate the trunk port to use for forwarding traffic by implementing the load distribution algorithm on
value equals to modulus of (XOR of last 3 bits of Source and last 3 bits of Destination IP address). For non-IP
traffic, the GbE2 Interconnect Switch will calculate the trunk port to use for forwarding traffic by implementing the
load distribution algorithm on value equals to modulus of (XOR of last 3 bits of Source and last 3 bits
of Destination MAC address).
Multicast, broadcast, and unknown unicast are forwarded on the first STP port in the trunk group that comes
online (usually the lowest port number in the trunk). If that link in the trunk fails, the next link (lowest port number)
in the trunk is used. If the link is restored, traffic will not be re-routed to the lowest link until the current link fails
again.
Built-in fault tolerance
Since each trunk group is composed of multiple physical links, the trunk group is inherently fault tolerant. As long
as even one physical link between the switches is available, the trunk remains active.
Statistical load distribution is maintained whenever a link in a trunk group is lost or returned to service.
Before you configure trunks
When you create and enable a trunk, the trunk members (GbE2 Interconnect Switch ports) take on certain
settings necessary for correct operation of the trunking feature.
Before you configure your trunk, you must consider these settings, along with specific configuration rules, as
follows:
1. Read the configuration rules provided in the “Trunk Group Configuration Rules” section.
2. Determine which GbE2 Interconnect Switch ports (up to six) are to become trunk members (the specific ports
making up the trunk).
3. Ensure that the chosen GbE2 Interconnect Switch ports are set to enabled, using the /cfg/port
command.
4. Trunk member ports must have the same VLAN configuration.
5. Consider how the existing spanning tree will react to the new trunk configuration. See the “Spanning Tree
Protocol” chapter for spanning tree group configuration guidelines.
6. Consider how existing VLANs will be affected by the addition of a trunk.