Port Configuration

With the Port Configuration window, you can:

Checking Port Configuration Settings

By default, all ports on a switch are enabled and port parameters are set with initial values. The Port Configuration window shows the current values for port parameter settings. For several parameters, this window contains two values: the value that the administrator sets and the value that is currently in effect on the port. All parameters can be changed on multiple ports simultaneously. See Port Configuration Settings for parameter descriptions.

Identifying an Autonegotiation Mismatch

An autonegotiation mismatch can occur under these conditions:

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 correct mismatched port settings, follow one of these suggestions:

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 works 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.

Changing Port Configuration Settings

To change port configuration parameters:

  1. From the port table on the Port Configuration window, select one or more ports to configure.
    To select several ports, hold down the Ctrl key and make your selections; or, hold down the Shift key and select the first and last port in a range.
  2. Click Modify to display the Port Configuration dialog box.
  3. In the Description field on this dialog box, enter a description for the selected ports.
    Your description should help you identify the ports. For example, end stations might be a useful description. If you limit the length of your description to 13 characters or less, the entire description will fit in this field without scrolling.
  4. Select the remaining parameter settings from the drop-down lists in the dialog box.
    See Port Configuration Settings, Setting IEEE 802.1p Priority Tags, and Configuring Flow Control on Gigabit Ethernet Ports for information on parameter settings if you need help.
  5. Click OK to put your changes in effect and close the Port Configuration dialog box.
    Your new settings are displayed in the Port Configuration window.
  6. Click OK to close the Port Configuration window.

Note: If you select multiple ports and specify a configuration setting that is not valid for a selected port, the current setting remains unchanged. For example, if you select a 10BaseT Ethernet, a FastEthernet, and a Gigabit port and then select a speed of 100 Mbps, the 10BaseT Ethernet port will remain set to 10 Mbps and the Gigabit port will remain set to 1000 Mbps.

Port Configuration Settings

Some port types automatically negotiate configuration settings; however, autonegotiating can produce unpredictable results. See Identifying an Autonegotiation Mismatch for more information.

Field Description
Interface
(read-only)		 Identifies the port: FastEthernet, Gigabit Ethernet, ATM, or FDDI, the module or slot number (0, 1, or 2), and the port number.
Status (Admin) Administrator setting to enable or disable the port, which can be different from the actual setting. For example, if no device is connected to a port, it can be administratively enabled with an actual status of DOWN.
Note: When you disable a port, a "linkdown" trap is sent to the management station if you configured an SNMP manager.
Status (Actual)
(read-only)		 Current state of the port. The status of a port can be up, down, or administratively down.
Duplex  (Admin) Administrator setting for duplex: full duplex, half duplex, or autosensing. The default setting for Gigabit Ethernet and GigaStack GBIC ports is auto. These ports automatically match the duplex capability of an attached device.
GigaStack GBIC stack connections operate in half-duplex mode.
Point-to-point GigaStack GBIC port connections operate in full-duplex mode.
Gigabit Ethernet ports can automatically match the duplex capability of an attached device. ATM ports do not autonegotiate Duplex or speed settings.
Duplex (Actual)
(read-only)		 Current duplex state of the port.
For ATM ports, this field is read-only and displays Full.
Speed (Admin) Administrator setting for Fast Ethernet ports: "10" (10 Mbps), "100" (100 Mbps), or "auto" (autonegotiating). Fast Ethernet ports can automatically match the transmission speed of an attached device. The default setting for Fast Ethernet ports is auto.
Speed (Actual)
(read-only)		 Current speed of the port.
For Gigabit Ethernet ports, this field is read-only and displays "1000" (1000 Mbps).
For ATM ports, this field is read-only and displays "155" (155 Mbps).
Port Fast Immediately brings a port from the blocking state into the forwarding state by eliminating the forwarding delay (the amount of time a port waits before changing from its Spanning-Tree Protocol (STP) learning and listening states to the forwarding state).
802.1p Assigns a priority to traffic containing an 802.1p or ISL user priority tag. To direct this traffic to a high priority queue, assign a value of 4 through 7. To direct this traffic to a normal queue, assign a value of 0 through 3. The switch forwards normal traffic only after it forwards all high priority traffic. On 2900 and 3500 XL switch ports, these settings also apply to untagged (native Ethernet) traffic.
Description Description of the port that helps to identify it. For example, server connection.
Flow Control On Gigabit Ethernet ports, enables or disables flow control, which manages traffic rates during congestion. (This parameter does not apply to Fast Ethernet or ATM ports.) If a port experiences congestion and cannot receive any more traffic, flow control notifies the other port to stop transmitting until the condition clears.
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.
Select None to disable flow control on the port.
Select Symmetric to have the local port perform flow control on the remote port. This option works only if the remote port can also perform flow control on the local port.
Select Asymmetric to have the local port 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.
Select Any when the local port can support any level of flow control required by the remote port.
This field is displayed only if Gigabit Ethernet ports are present; it does not apply to Fast Ethernet or ATM ports.
Power (Admin) (Catalyst 3524-PWR XL switch only) Administrator setting for a Fast Ethernet port used for telephone connections: if set to "Auto," the switch automatically detects a telephone on the port and applies power to it; if set to "Never," the switch does not apply power to the port, even if a telephone is connected.
Power (Actual) (Catalyst 3524-PWR XL switch only) Current state of a Fast Ethernet port used for telephone connections. If the administrator setting is "Auto," "Yes" means that the switch detects a telephone and is applying power to the port; "No" means that no telephone is detected and no power is being applied. If the administrator setting is "Never," this column always contains "No."

Setting  IEEE 802.1Q Priority Tags

You can configure quality of service (QoS) for traffic containing IEEE 802.1Q 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.

Catalyst 1900 and 2820 switches, Catalyst 2924 and 2924C XL switches with only 4 MB of memory, and switches running IOS Release 11.2 (8)SA6 or earlier do not support 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.

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.

Options in the Flow Control drop-down list have the following meaning:
None: disables flow control on the port.
Symmetric: enables the local port to perform flow control on 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.