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Port Status and Basic Configuration
QoS Pass-Through Mode on the Series 2800 Switches
Troubleshooting
A VLAN is configured to allow jumbo packets, but one or more ports
drops all inbound jumbo packets. The port may not be operating at 1
gigabit or higher. Regardless of a port’s configuration, if it is actually operating
at a speed lower than 1 gigabit, it drops inbound jumbo packets. For example,
if a port is configured for Auto mode (speed-duplex auto), but has negotiated a
100 Mbps speed with the device at the other end of the link, then the port
cannot receive inbound jumbo packets. To determine the actual operating
speed of one or more ports, view the Mode field in the output for the following
command:
show interfaces brief < port-list >
A non-jumbo port is generating “Excessive undersize/giant packets”
messages in the Event Log. The 2800 switch can transmit outbound jumbo
traffic on any port, regardless of whether the port belongs to a jumbo VLAN.
In this case, another port in the same VLAN on the 2800 switch may be jumbo-
enabled through membership in a different, jumbo-enabled VLAN, and may
be forwarding jumbo packets received on the jumbo VLAN to non-jumbo
ports. Refer to “Outbound Jumbo Traffic” on page
10-23.
QoS Pass-Through Mode on the Series
2800 Switches
Release I.07.52 introduced a new command to enhance the performance of
line-rate traffic transfers through the Series 2800 switches. This feature should
only be used in environments where Quality of Service (QoS) is not of major
importance, but where lossless data transfers are key. This command essen-
tially disables any discrimination of QoS queues for traffic, consolidating
packet buffer memory to provide line-rate flows with no loss of data.
General Operation
The port buffering design for the Series 2800 switches has been optimized for
gigabit-to-gigabit traffic flows. For this reason, some flows from Gigabit-to-
100Base or even 100Base-to-10Base may not perform as well as would be
expected. The QoS Pass-Through mode enhancement can provide a signifi-
10-25