Port Configuration

With the Port Configuration page, you can:

• Disable a port.
• Name a port.
• Change the duplex and transmission speed settings.
• Set IEEE 802.1p priority tags (Enterprise Edition Software only).
• Identify an autonegotiation mismatch.
• Configure flow control on Gigabit Ethernet ports.
• Display port performance statistics.

For information about the fields on this page, review the Field Descriptions.

Disabling a Port

All ports are enabled by default.

To administratively disable a port:

1. In the Status: Admin/Actual column, deselect the Enable checkbox.
   This column displays the actual status of the port. An enabled port could have an actual status of DOWN if no device is connected to it.
2. Click Apply.
   A "linkdown" trap is sent to the management station if you configured an SNMP manager.

Changing the Duplex and Transmission Speed Settings

Fast Ethernet ports can automatically match the duplex capability and the transmission speed of an attached device. Gigabit Ethernet ports can automatically match the duplex capability of an attached device. ATM ports do not autonegotiate duplex or speed settings.

Note: Changing the port configuration can cause the Spanning-Tree Protocol (STP) to check for a new loop. While STP reconfigures, the port LED is amber for about 30 seconds.

To change the duplex and transmission speed settings:

1. From the Duplex: Requested/Actual drop-down list, select Half, Full, or Auto (autonegotiating).
   The default setting for Fast Ethernet, Gigabit Ethernet, and GigaStack GBIC ports is Auto.
   Note: For ATM ports, this field is read-only and displays "Full" for full duplex.
   Note: Point-to-point GigaStack GBIC port connections operate in full-duplex mode. GigaStack GBIC stack connections operate in half-duplex mode.
2. From the Speed: Requested/Actual drop-down list, select 10 (10 Mbps), 100 (100 Mbps), or Auto (autonegotiating).
   The default is Auto for Fast Ethernet ports.
   Note: For Gigabit Ethernet ports, this field is read-only and displays "1000" for 1000 Mbps. For ATM ports, this field is read-only and displays "155" for 155 Mbps.
3. Click Apply.

Autonegotiating can produce unpredictable results. For more information, see Identifying an Autonegotiation Mismatch.

Identifying an Autonegotiation Mismatch

An autonegotiation mismatch can occur under these conditions:

• When a manually set duplex parameter is different from that set on the attached port
• When port is set to autonegotiate and the attached port is set to full duplex with no autonegotiation

The result of a mismatch on Fast Ethernet ports is reduced performance or link errors. On Gigabit Ethernet ports, the link does not come up and no statistics are reported.

To identify and confirm an autonegotiation mismatch when the Fast Ethernet port is in half-duplex mode:

1. In the Statistics column, click View for the switch port, and check for late-collision errors.
2. Check the attached port.
   If it is in full-duplex mode, a mismatch exists.
3. Click View to check for FCS errors on the full-duplex port, and to check for late collisions on the half-duplex port.
4. Compare your findings with the following principles:

• Late collisions or no link errors indicate that a port set to half duplex is connected to a port set to full duplex.
• FCS errors indicate that a port set to full duplex is connected to a port set to half duplex.

To correct mismatched port settings, follow one of these suggestions:

• Let both ports autonegotiate both speed and duplex.
• Manually set the speed and duplex parameters for the ports on both ends of the connection.

Note: To connect to a remote Fast Ethernet device that does not autonegotiate, you should explicitly set the duplex on the local device to a value other than Auto. Speed negotiation will work even if the other device does not autonegotiate. To connect to a remote Gigabit Ethernet device that does not autonegotiate, disable autonegotiation on the local device and set the duplex and flow control parameters to be compatible with the remote device.

Setting  IEEE 802.1p Priority Tags

With Enterprise Edition Software, you can configure quality of service (QoS) for traffic containing IEEE 802.1p or ISL user priority tags. When the switch receives tagged traffic, it transfers the traffic to two queues: a normal queue receives frames with priority values from 0 to 3; and a high priority queue receives frames with priority values from 4 to 7. Traffic on the normal queue is forwarded only after traffic on the high priority queue is forwarded.

Catalyst 2900 and 3500 XL switches can also provide QoS on untagged (native Ethernet) traffic, based on a priority level that you assign to the ingress port (the receiver queue buffer for incoming traffic). If you assign a port priority level from 0 to 3, traffic is forwarded to the normal priority queue of  the output port. If you assign a priority level from 4 to 7, traffic is forwarded to the high priority queue of  the output port. When 802.1p or ISL tagged traffic passes through the trunk port, it retains the 802.1p or ISL tag. (See the Cisco IOS Desktop Switching Enterprise Edition Software Configuration Guide for details.)

Switches running standard edition software must be upgraded to Enterprise Edition Software to use priority tags. (Catalyst 2924 and Catalyst 2924C XL switches that contain only 4 MB of memory do not support port priority levels.)

Note: If you are connecting to a switch in the Catalyst 6000 family, the switch must be configured for compatibility with 2900 and 3500 XL switches. Refer to your Catalyst 6000 documentation for information on making the necessary changes.

To assign a priority level to a port:

1. In the 802.1p Default Priority column, select a priority level from the drop-down list.
2. Click Apply.

Naming a Port

To name a port:

1. In the Port Name column, enter a name or a description of how the port is connected.
2. Click Apply.

Displaying Port Performance Statistics

To display port performance statistics, click View for the selected port in the Statistics column. A separate browser window launches containing transmit and receive statistics for the port.

Note: You can clear the statistics by clicking Reset. Clicking the Reset button also closes the statistics page and refreshes the Port Configuration page.

Field Descriptions

Configuring Flow Control on Gigabit Ethernet Ports

Flow control enables the connected Gigabit Ethernet ports (including GBICs and GigaStack GBICs) to control traffic rates during congestion. If one port experiences congestion and cannot receive any more traffic, it notifies the other port to stop transmitting until the condition clears.

Note: This field is displayed only if Gigabit Ethernet ports are present; it does not apply to Fast Ethernet or ATM ports.

To configure flow control on a Gigabit Ethernet port:

1. In the Flow Control drop-down list, select one of these options:
   None: disables flow control on the port.
   Symmetric: enables the local port to perform flow control of the remote port only if the remote port can also perform flow control on the local port.
   Asymmetric: enables the local port to perform flow control on the remote port. For example, if the local port is congested, it notifies the remote port to stop transmitting. This setting is the default.
   Any: enables the local port to support any level of flow control required by the remote port.
   Note: By default, when the GigaStack GBIC is in a stack configuration (daisy chain), flow control is disabled. When the GigaStack GBIC is in a point-to-point configuration, flow control is set to asymmetric, the same setting for GBICs in general.
2. Click Apply.