Catalyst 6500 Release 12.2SY Software Configuration Guide

Configuring Ethernet Interface Speed and Duplex Mode

• Speed and Duplex Mode Configuration Guidelines
• Configuring the Ethernet Interface Speed
• Setting the Interface Duplex Mode
• Configuring Link Negotiation on Gigabit Ethernet Ports
• Displaying the Speed and Duplex Mode Configuration

Speed and Duplex Mode Configuration Guidelines

You usually configure Ethernet port speed and duplex mode parameters to auto and allow ports to negotiate the speed and duplex mode. If you decide to configure the port speed and duplex modes manually, consider the following information:

• You cannot set the Ethernet port speed to auto (the no speed command) if the duplex mode in not set to auto (the no duplex command).
• If you configure an Ethernet port speed to a value other than auto (for example, 10, 100, or 1000 Mbps), configure the connecting port to match. Do not configure the connecting port to negotiate the speed.
• If you manually configure the Ethernet port speed to either 10 Mbps or 100 Mbps, the switch prompts you to also configure the duplex mode on the port.

Note A LAN port cannot automatically negotiate Ethernet port speed and duplex mode if the connecting port is configured to a value other than auto.

Caution Changing the Ethernet port speed and duplex mode configuration might shut down and reenable the interface during the reconfiguration.

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Configuring the Ethernet Interface Speed

Note If you configure the Ethernet port speed to auto on a 10/100/1000-Mbps Ethernet port, both speed and duplex are autonegotiated. 10-Gigabit Ethernet ports do not support autonegotiation.

To configure the port speed for a 10/100/1000-Mbps Ethernet port, perform this task:

When configuring the port speed for a 10/100/1000-Mbps Ethernet port, note the following:

• Enter the auto 10 100 keywords to restrict the negotiated speed to 10-Mbps or 100-Mbps.
• The auto 10 100 1000 keywords have the same effect as the auto keyword by itself.

This example shows how to configure the speed to 100 Mbps on the Gigabit Ethernet port 1/4:

Setting the Interface Duplex Mode

Note ● 10-Gigabit Ethernet and Gigabit Ethernet are full duplex only. You cannot change the duplex mode on 10-Gigabit Ethernet or Gigabit Ethernet ports or on a 10/100/1000-Mps port configured for Gigabit Ethernet.

• If you set the port speed to auto on a 10/100/1000-Mbps Ethernet port, both speed and duplex are autonegotiated. You cannot change the duplex mode of autonegotiation ports.

To set the duplex mode of an Ethernet or Gigabit Ethernet port, perform this task:

This example shows how to set the duplex mode to full on Gigabit Ethernet port 1/4:

Configuring Link Negotiation on Gigabit Ethernet Ports

Note Link negotiation does not negotiate port speed.

On Gigabit Ethernet ports, link negotiation exchanges flow-control parameters, remote fault information, and duplex information. Link negotiation is enabled by default.

The ports on both ends of a link must have the same setting. The link will not come up if the ports at each end of the link are set inconsistently (link negotiation enabled on one port and disabled on the other port).

Table 10-1 shows the four possible link negotiation configurations and the resulting link status for each configuration.

To configure link negotiation on a port, perform this task:

This example shows how to enable link negotiation on Gigabit Ethernet port 1/4:

Displaying the Speed and Duplex Mode Configuration

To display the speed and duplex mode configuration for a port, perform this task:

Configuring Jumbo Frame Support

• Information about Jumbo Frame Support
• Configuring MTU Sizes

Information about Jumbo Frame Support

• Jumbo Frame Support Overview
• Nondefault MTU Sizes on Ethernet Ports
• VLAN Interfaces

Jumbo Frame Support Overview

A jumbo frame is a frame larger than the default Ethernet size. You enable jumbo frame support by configuring a larger-than-default maximum transmission unit (MTU) size on a port or VLAN interface and configuring the global LAN port MTU size.

Note ● Jumbo frame support fragments routed traffic in software on the route processor (RP).

• Jumbo frame support does not fragment bridged traffic.

Bridged and Routed Traffic Size Check at Ingress 10/100, and 100 Mbps Ethernet and 10-Gigabit Ethernet Ports

Jumbo frame support compares ingress traffic size with the global LAN port MTU size at ingress 10/100, and 100 Mbps Ethernet and 10-Gigabit Ethernet LAN ports that have a nondefault MTU size configured. The port drops traffic that is oversized. You can configure the global LAN port MTU size (see the “Configuring the Global Egress LAN Port MTU Size” section).

Bridged and Routed Traffic Size Check at Ingress Gigabit Ethernet Ports

Gigabit Ethernet LAN ports configured with a nondefault MTU size accept frames containing packets of any size larger than 64 bytes. With a nondefault MTU size configured, Gigabit Ethernet LAN ports do not check for oversize ingress frames.

Routed Traffic Size Check on the PFC

For traffic that needs to be routed, Jumbo frame support on the PFC compares traffic sizes to the configured MTU sizes and provides Layer 3 switching for jumbo traffic between interfaces configured with MTU sizes large enough to accommodate the traffic. Between interfaces that are not configured with large enough MTU sizes, if the “do not fragment bit” is not set, the PFC sends the traffic to the RP to be fragmented and routed in software. If the “do not fragment bit” is set, the PFC drops the traffic.

Bridged and Routed Traffic Size Check at Egress 10, 10/100, and 100 Mbps Ethernet Ports

10, 10/100, and 100 Mbps Ethernet LAN ports configured with a nondefault MTU size transmit frames containing packets of any size larger than 64 bytes. With a nondefault MTU size configured, 10, 10/100, and 100 Mbps Ethernet LAN ports do not check for oversize egress frames.

Bridged and Routed Traffic Size Check at Egress Gigabit Ethernet and 10-Gigabit Ethernet Ports

Jumbo frame support compares egress traffic size with the global egress LAN port MTU size at egress Gigabit Ethernet and 10-Gigabit Ethernet LAN ports that have a nondefault MTU size configured. The port drops traffic that is oversized. You can configure the global LAN port MTU size (see the “Configuring the Global Egress LAN Port MTU Size” section).

Nondefault MTU Sizes on Ethernet Ports

• Ethernet Port Overview
• Layer 3 Ethernet Ports
• Layer 2 Ethernet Ports

Ethernet Port Overview

Configuring a nondefault MTU size on a 10, 10/100, or 100 Mbps Ethernet port limits ingress packets to the global LAN port MTU size and permits egress traffic of any size larger than 64 bytes.

Configuring a nondefault MTU size on a Gigabit Ethernet port permits ingress packets of any size larger than 64 bytes and limits egress traffic to the global LAN port MTU size.

Configuring a nondefault MTU size on a 10-Gigabit Ethernet port limits ingress and egress packets to the global LAN port MTU size.

You can configure the MTU size on any Ethernet port.

Layer 3 Ethernet Ports

On a Layer 3 port, you can configure an MTU size on each Layer 3 Ethernet port that is different than the global LAN port MTU size.

Note Traffic through a Layer 3 Ethernet LAN port that is configured with a nondefault MTU size is also subject to the global LAN port MTU size (see the “Configuring the Global Egress LAN Port MTU Size” section).

Layer 2 Ethernet Ports

On a Layer 2 port, you can only configure an MTU size that matches the global LAN port MTU size (see the “Configuring the Global Egress LAN Port MTU Size” section).

VLAN Interfaces

You can configure a different MTU size on each Layer 3 VLAN interface. Configuring a nondefault MTU size on a VLAN interface limits traffic to the nondefault MTU size. You can configure the MTU size on VLAN interfaces to support jumbo frames.

Configuring MTU Sizes

• Configuring the MTU Size
• Configuring the Global Egress LAN Port MTU Size

Configuring the MTU Size

To configure the MTU size, perform this task:

When configuring the MTU size, note the following information:

• For VLAN interfaces and Layer 3 Ethernet ports, supported MTU values are from 64 to 9216 bytes.
• For Layer 2 Ethernet ports, you can configure only the global egress LAN port MTU size (see the “Configuring the Global Egress LAN Port MTU Size” section).
• MTU size on a Layer 2 interface is always set to maximum. If you reconfigure the MTU size to enable jumbo frame support, MTU size does not get updated in the MTU hardware table for L2 interface at the egress. The interface (L2) MTU size check happens only at the ingress port.

This example shows how to configure the MTU size on Gigabit Ethernet port 1/2:

This example shows how to verify the configuration:

Configuring the Global Egress LAN Port MTU Size

To configure the global egress LAN port MTU size, perform this task:

Configuring IEEE 802.3x Flow Control

Gigabit Ethernet and 10-Gigabit Ethernet ports use flow control to stop the transmission of frames to the port for a specified time; other Ethernet ports use flow control to respond to flow-control requests.

If a Gigabit Ethernet or 10-Gigabit Ethernet port receive buffer becomes full, the port can be configured to transmit an IEEE 802.3x pause frame that requests the remote port to delay sending frames for a specified time. All Ethernet ports can can be configured to respond to IEEE 802.3x pause frames from other devices.

To configure flow control on an Ethernet port, perform this task:

When configuring flow control, note the following information:

• Because auto negotiation does not work on 10 Gigbit Ethernet fiber optic ports, they respond to pause frames by default. On 10 Gigbit Ethernet fiber optic ports, the flow-control operational mode is always the same as administrative mode.
• When configuring how a port responds to pause frames, note the following information:

– For a Gigabit Ethernet port, when the configuration of a remote port is unknown, you can use the receive desired keywords to configure the Gigabit Ethernet port to respond to received pause frames. (Supported only on Gigabit Ethernet ports.)

– Use the receive on keywords to configure a port to respond to received pause frames.

– Use the receive off keywords to configure a port to ignore received pause frames.

• When configuring transmission of pause frames on a port, note the following information:

– For a Gigabit Ethernet port, when the configuration of the remote ports is unknown, you can use the send desired keywords to configure the Gigabit Ethernet port to send pause frames. (Supported only on Gigabit Ethernet ports.)

– Use the send on keywords to configure a port to send pause frames.

– Use the send off keywords to configure a port not to send pause frames.

This example shows how to turn on receive flow control and how to verify the flow-control configuration:

Configuring the Port Debounce Timer

The port debounce timer delays notification of a link change, which can decrease traffic loss due to network reconfiguration. You can configure the port debounce timer separately on each LAN port.

Caution Enabling the port debounce timer causes link down detections to be delayed, resulting in loss of traffic during the debouncing period. This situation might affect the convergence and reconvergence of some Layer 2 and Layer 3 protocols.

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To configure the debounce timer on a port, perform this task:

When configuring the debounce timer on a port, note the following information:

• The time keyword is supported only on fiber 1000 Mpbs or faster Ethernet ports.
• You can increase the port debounce timer value in increments of 100 milliseconds up to 5000 milliseconds on ports operating at 1000 Mpbs over copper media.
• The debounce timer recognizes 10-Gbps copper media and detects media-only changes.

Table 10-2 lists the time delay that occurs before notification of a link change.

Note On all 10-Gigabit Ethernet ports, the Debounce Timer Disabled value is 10 milliseconds and the Debounce Timer Enabled value is 100 milliseconds.

This example shows how to enable the port debounce timer on Gigabit Ethernet port 1/12:

This example shows how to display the port debounce timer settings:

Monitoring Interface Status

The software contains commands that you can enter at the EXEC prompt to display information about the interface including the version of the software and the hardware and statistics about interfaces. The following table lists some of the interface monitoring commands. (You can display the complete list of show commands by using the show ? command at the EXEC prompt.) These commands are described in the Cisco IOS Interface Command Reference publication.

To display information about the interface, perform these tasks:

Clearing Counters on an Interface

To clear the interface counters shown with the show interfaces command, perform this task:

This example shows how to clear and reset the counters on Gigabit Ethernet port 1/5:

The clear counters command clears all the current counters from the interface unless the optional arguments specify a specific interface.

Note The clear counters command clears counters displayed with the EXEC show interfaces command, not counters retrieved using SNMP.

Resetting an Interface

To reset an interface, perform this task:

This example shows how to reset Gigabit Ethernet port 1/5:

Shutting Down and Restarting an Interface

You can shut down an interface, which disables all functions on the specified interface and shows the interface as unavailable on all monitoring command displays. This information is communicated to other network servers through all dynamic routing protocols. The interface is not included in any routing updates.

To shut down an interface and then restart it, perform this task:

This example shows how to shut down Gigabit Ethernet port 1/5:

Note The link state messages (LINK-3-UPDOWN and LINEPROTO-5-UPDOWN) are disabled by default. Enter the logging event link status command on each interface where you want the messages enabled.

This example shows how to reenable Gigabit Ethernet port 1/5:

To check if an interface is disabled, enter the EXEC show interfaces command. An interface that has been shut down is shown as administratively down in the show interfaces command display.