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34 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring basic port parameters
2
Maximum Port speed advertisement and Port speed down-shift are enhancements to the
auto-negotiation feature, a mechanism for accommodating multi-speed network devices by
automatically configuring the highest performance mode of inter-operation between two connected
devices.
Port speed down-shift enables Gbps copper ports on the Dell PowerConnect device to establish a
link at 1000 Mbps over a 4-pair wire when possible, or to down-shift to 100 Mbps if the medium is
a 2-pair wire.
Maximum port speed advertisement enables you to configure an auto-negotiation maximum speed
that Gbps copper ports on the Dell PowerConnect device will advertise to the connected device.
You can configure a port to advertise a maximum speed of either 100 Mbps or 10 Mbps. When the
maximum port speed advertisement feature is configured on a port that is operating at 100 Mbps
maximum speed, the port will advertise 10/100 Mbps capability to the connected device.
Similarly, if a port is configured at 10 Mbps maximum speed, the port will advertise 10 Mbps
capability to the connected device.
The port speed down-shift and maximum port speed advertisement features operate dynamically
at the physical link layer between two connected network devices. They examine the cabling
conditions and the physical capabilities of the remote link, then configure the speed of the link
segment according to the highest physical-layer technology that both devices can accommodate.
The port speed down-shift and maximum port speed advertisement features operate dynamically
at the physical link layer, independent of logical trunk group configurations. Although Dell
recommends that you use the same cable types and auto-negotiation configuration on all
members of a trunk group, you could utilize the auto-negotiation features conducive to your cabling
environment. For example, in certain circumstances, you could configure each port in a trunk
group to have its own auto-negotiation maximum port speed advertisement or port speed
down-shift configuration.
Application notes
• Port speed down-shift and maximum port speed advertisement work only when
auto-negotiation is enabled (CLI command speed-duplex auto). If auto-negotiation is OFF, the
device will reject the port speed down-shift and maximum port speed advertisement
configuration.
• When port speed down-shift or maximum port speed advertisement is enabled on a port, the
device will reject any configuration attempts to set the port to a forced speed mode (100 Mbps
or 1000 Mbps).
• When the port speed down-shift feature is enabled on a combo port, the port will not support
true media automatic detection, meaning the device will not be able to detect and select the
fiber or copper connector based on link availability.
Enabling port speed down-shift
To enable port speed down-shift on a port that has auto-negotiation enabled, enter a command
such as the following at the Global CONFIG level of the CLI.
PowerConnect(config)# link-config gig copper autoneg-control down-shift ethernet
1 ethernet 2
The above command configures Gbps copper ports 1 and 2 to establish a link at 1000 Mbps over a
4-pair wire when possible, or to down-shift (reduce the speed) to 100 Mbps when the medium is a
2-pair wire.