HP 6120XG ProCurve Series 6120 Blade Switches Management and Configuration Gui - Page 347

Port Traffic Controls Cut-Through Switching on the HP 6120XG Troubleshooting A VLAN is configured to allow jumbo frames, but one or more ports drops all inbound jumbo frames. The port may not be operating at 1 giga­ bit or higher. Regardless of a port's configuration, if it is actually operating at a speed lower than 1 gigabit, it drops inbound jumbo frames. 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 frames. 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 frames" messages in the Event Log. The switches 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 switch may be jumboenabled through membership in a different, jumbo-enabled VLAN, and may be forwarding jumbo frames received on the jumbo VLAN to non-jumbo ports. Refer to "Outbound Jumbo Traffic" on page 12-28. Cut-Through Switching on the HP 6120XG Switches using store and forward mode wait to receive the entire frame before forwarding it. Switches using cut-through mode forward the frame when enough of the frame has been received to identify the output port. This mode can reduce latency in frame delivery. The drawback of cut-through mode is that frames are forwarded before any CRC errors are detected. The HP 6120XG switch supports cut-through switching. When enabled, it applies globally; all ports operate in cut-through mode or store-and-forward mode. Enabling or disabling cut-through mode requires a reboot of the switch. Syntax: [no] cut-through Globally enables or disables cut-through mode on the switch. Default: Disabled 12-29