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