Cisco Nexus 4001I and 4005I Switch Module for IBM BladeCenter NX-OS Configuration Guide

About the Interface Command

You can enable the various capabilities of the Ethernet interfaces on a per-interface basis using the interface command. When you enter the interface command, you specify the following information:

• Interface type—All physical Ethernet interfaces use the ethernet keyword.
• Slot number

– Slot 1 includes up to 20 ports.

• Port number

– Port number within the group.

About the Unidirectional Link Detection Parameter

This section includes the following topics:

• UDLD Overview
• Default UDLD Configuration
• UDLD Aggressive and Nonaggressive Modes

UDLD Overview

The Cisco-proprietary Unidirectional Link Detection (UDLD) protocol allows ports that are connected through fiber optics or copper (for example, Category 5 cabling) Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. When the switch detects a unidirectional link, UDLD shuts down the affected LAN port and alerts the user. Unidirectional links can cause a variety of problems, including spanning tree topology loops.

UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected LAN ports. When you enable both autonegotiation and UDLD, Layer 1 and Layer 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.

A unidirectional link occurs whenever traffic transmitted by the local device over a link is received by the neighbor but traffic transmitted from the neighbor is not received by the local device. If one of the fiber strands in a pair is disconnected, as long as autonegotiation is active, the link does not stay up. In this case, the logical link is undetermined, and UDLD does not take any action. If both fibers are working normally at Layer 1, then UDLD at Layer 2 determines whether those fibers are connected correctly and whether traffic is flowing bidirectionally between the correct neighbors. This check cannot be performed by autonegotiation, because autonegotiation operates at Layer 1.

The switch periodically transmits UDLD frames to neighbor devices on LAN ports with UDLD enabled. If the frames are echoed back within a specific time frame and they lack a specific acknowledgment (echo), the link is flagged as unidirectional and the LAN port is shut down. Devices on both ends of the link must support UDLD in order for the protocol to successfully identify and disable unidirectional links.

Note By default, UDLD is locally disabled on copper LAN ports to avoid sending unnecessary control traffic on this type of media.

Figure 5-1 shows an example of a unidirectional link condition. Device B successfully receives traffic from device A on the port. However, device A does not receive traffic from device B on the same port. UDLD detects the problem and disables the port.

Figure 5-1 Unidirectional Link

Default UDLD Configuration

Table 5-1 shows the default UDLD configuration.

For information on configuring the UDLD for the device and its port, see the “Configuring the UDLD Mode” section.

UDLD Aggressive and Nonaggressive Modes

UDLD aggressive mode is disabled by default. You can configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. If UDLD aggressive mode is enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD frames, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled.

To prevent spanning tree loops, nonaggressive UDLD with the default interval of 15 seconds is fast enough to shut down a unidirectional link before a blocking port transitions to the forwarding state (with default spanning tree parameters).

When you enable the UDLD aggressive mode, the following occurs:

• One side of a link has a port stuck (both transmission and receive)
• One side of a link remains up while the other side of the link is down

In these cases, the UDLD aggressive mode disables one of the ports on the link, which prevents traffic from being discarded.

About Interface Speed

The switch has external and internal switchable 10-Gigabit and 1-Gigabit Ethernet ports. Each port is equipped with SFP+ interface adapters.

About the Cisco Discovery Protocol

CDP is a device discovery protocol that runs over Layer 2 (the data link layer) on all Cisco-manufactured devices (routers, bridges, access servers, and switches) and allows network management applications to discover Cisco devices that are neighbors of already known devices. With CDP, network management applications can learn the device type and the Simple Network Management Protocol (SNMP) agent address of neighboring devices running lower-layer, transparent protocols. This feature enables applications to send SNMP queries to neighboring devices.

CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CDP runs over the data-link layer only, two systems that support different network-layer protocols can learn about each other.

Each CDP-configured device sends periodic messages to a multicast address, advertising at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime information, which is the length of time a receiving device holds CDP information before discarding it. Each device also listens to the messages sent by other devices to learn about neighboring devices.

The switch supports both CDP Version 1 and Version 2.

Default CDP Configuration

Table 5-2 shows the default CDP configuration.

About the Debounce Timer Parameters

The port debounce time is the amount of time that an interface waits to notify that a link is going down. During this time, the interface waits to see if the link comes back up. The wait period is a time when traffic is stopped.

You can enable the debounce timer for each interface and specify the delay time in milliseconds.

Caution When you enable the port debounce timer the link up and link down detections are delayed, resulting in a loss of traffic during the debounce period. This situation might affect the convergence and reconvergence of some protocols.

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About MTU Configuration

A per-physical Ethernet interface maximum transmission unit (MTU) is not supported. Instead, MTU is set according to the QoS classes. You modify MTU by setting Policy and Class maps. See Chapter 30, “Configuring Quality of Service” for more details.

When you show the interface settings, an MTU of 1500 is displayed for physical Ethernet interfaces.

Configuring the UDLD Mode

You can configure normal or aggressive unidirectional link detection (UDLD) modes for Ethernet interfaces on devices configured to run UDLD. Before you can enable a UDLD mode for an interface, you must make sure that UDLD is already enabled on the device that includes the interface. UDLD must also be enabled on the other linked interface and its device.

To use the normal UDLD mode, you must configure one of the ports for normal mode and configure the other port for the normal or aggressive mode. To use the aggressive UDLD mode, you must configure both ports for the aggressive mode.

Note Before you begin, UDLD must be enabled for the other linked port and its device.

To configure the UDLD mode, perform this task:

The following example shows how to enable the UDLD for the switch:

The following example shows how to enable the normal UDLD mode for an Ethernet port:

The following example shows how to enable the aggressive UDLD mode for an Ethernet port:

The following example shows how to disable UDLD for an Ethernet port:

The following example shows how to disable UDLD for the switch:

Configuring Interface Speed

The switch supports 6 switchable 1-Gigabit and 10-Gigabit ports. The default interface speed is 10-Gigabit. To configure these ports for 1-Gigabit Ethernet, insert a 1-Gigabit Ethernet SFP transceiver into the applicable port and then set its speed with the speed command.

To configure a 1-Gigabit Ethernet port, perform this task:

The following example shows how to set the speed for a 1-Gigabit Ethernet port:

This command can only be applied to a physical Ethernet interface.

Note If the interface and transceiver speed is mismatched, the SFP validation failed message is displayed when you enter the show interface ethernet slot/port command. For example, if you insert a 1-Gigabit SFP transceiver into a port without configuring the speed 1000 command, you will get this error. By default, all ports are 10 Gigabits.

Configuring the Cisco Discovery Protocol

This section shows how to configure the Cisco Discovery Protocol (CDP). It includes the following topics:

• Configuring the CDP Characteristics
• Enabling or Disabling CDP

Configuring the CDP Characteristics

You can configure the frequency of CDP updates, the amount of time to hold the information before discarding it, and whether or not to send Version-2 advertisements.

To configure CDP characteristics for an interface, perform this task:

Use the no form of the CDP commands to return to the default settings.

The following example shows how to configure CDP characteristics:

Enabling or Disabling CDP

You can enable or disable CDP for Ethernet interfaces. This protocol works only when you have it enabled on both interfaces on the same link.

To enable or disable CDP for an interface, perform this task:

The following example shows how to enable CDP for an Ethernet port:

This command can only be applied to a physical Ethernet interface.

Configuring the Debounce Timer

You can enable the debounce timer for Ethernet ports by specifying a debounce time (in milliseconds) or disable the timer by specifying a debounce time of 0.

The debounce timer is enabled by default on all Ethernet ports and the value is set to 100 milliseconds.

You can show the debounce times for all of the Ethernet ports by using the show interface debounce command.

To enable or disable the debounce timer, perform this task:

The following example shows how to enable the debounce timer and set the debounce time to 1000 milliseconds for an Ethernet interface:

The following example shows how to disable the debounce timer for an Ethernet interface:

This command can only be applied to a physical Ethernet interface.

Configuring the Description Parameter

To provide textual interface descriptions for the Ethernet ports, perform this task:

The following example shows how to set the interface description to “Server 3 Interface”:

Disabling and Restarting Ethernet Interfaces

You can shut down and restart an Ethernet interface. This action disables all of the interface functions and marks the interface as being down on all monitoring displays. This information is communicated to other network servers through all dynamic routing protocols. When shut down, the interface is not included in any routing updates.

To disable an interface, perform this task:

The following example shows how to disable an Ethernet port:

To restart an interface, perform this task:

The following example shows how to restart an Ethernet interface:

Default Physical Ethernet Settings

The following table lists the default settings for all physical Ethernet interfaces.