Configuring Interface Characteristics

Table Of Contents

Configuring Interfaces

Understanding Interface Types

NNI Port Type

Port-Based VLANs

Switch Ports

Access Ports

Trunk Ports

Routed Ports

Ethernet Management Port

Switch Virtual Interfaces

EtherChannel Port Groups

Ethernet Flow Points

Connecting Interfaces

Using Interface Configuration Mode

Procedures for Configuring Interfaces

Configuring a Range of Interfaces

Configuring and Using Interface Range Macros

Using the Ethernet Management Port

Understanding the Ethernet Management Port

Supported Features on the Ethernet Management Port

Configuring the Ethernet Management Port

TFTP and the Ethernet Management Port

Configuring Ethernet Interfaces

Default Ethernet Interface Configuration

Configuring Interface Speed and Duplex Mode

Speed and Duplex Configuration Guidelines

Setting the Interface Speed and Duplex Parameters

Configuring IEEE 802.3x Flow Control

Configuring Auto-MDIX on an Interface

Adding a Description for an Interface

Configuring Layer 3 Interfaces

Configuring the Interface MTU

Monitoring and Maintaining the Interfaces

Monitoring Interface Status

Clearing and Resetting Interfaces and Counters

Shutting Down and Restarting the Interface

Configuring Interfaces

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This chapter defines the types of interfaces on the Cisco ME 3800X and ME 3600X switches and describes how to configure them.

•Understanding Interface Types

•Using Interface Configuration Mode

•Using the Ethernet Management Port

•Configuring Ethernet Interfaces

•Configuring Layer 3 Interfaces

•Configuring the Interface MTU

•Monitoring and Maintaining the Interfaces

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Note For complete syntax and usage information for the commands used in this chapter, see the switch command reference for this release and the online Cisco IOS Interface Command Reference, Release 12.2.

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Understanding Interface Types

This section describes the different types of interfaces supported by the switch with references to chapters that contain more detailed information about configuring these interface types. The rest of the chapter describes configuration procedures for physical interface characteristics.

•NNI Port Type

•Port-Based VLANs

•Switch Ports

•Routed Ports

•Ethernet Management Port

•Switch Virtual Interfaces

•EtherChannel Port Groups

•Connecting Interfaces

NNI Port Type

All Cisco ME 3800X and 3600X ports are network node interfaces (NNIs), which are typically connected to a router or to another switch. The default status for an NNI is administratively up to allow a service provider remote access to the switch during initial configuration.

Port-Based VLANs

A VLAN is a switched network that is logically segmented by function, team, or application, without regard to the physical location of the users. For more information about VLANs, see Chapter 11 "Configuring VLANs." Packets received on a port are forwarded only to ports that belong to the same VLAN as the receiving port. Network devices in different VLANs cannot communicate with one another without a Layer 3 device to route traffic between the VLANs.

VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC address table. A VLAN comes into existence when a local port is associated with the VLAN ID or when a user creates te VLAN ID.

To configure VLANs, use the vlan vlan-id global configuration command to enter VLAN configuration mode. The VLAN configurations for VLAN IDs 1 to 1005 are saved in the VLAN database. Extended-range VLANs (VLAN IDs 1006 to 4094) are not added to the VLAN database. VLAN configuration is saved in the switch running configuration, and you can save it in the switch startup configuration file by entering the copy running-config startup-config privileged EXEC command.

Add ports to a VLAN by using the switchport interface configuration commands:

•Identify the interface.

•For a trunk port, set trunk characteristics, and if desired, define the VLANs to which it can belong.

•For an access port, set and define the VLAN to which it belongs.

To isolate VLANs of different customers in a service-provider network, Cisco ME switches use UNI VLANs. Local switching does not occur among user network interfaces (UNIs) and enhanced network interfaces (ENIs) on the switch that belong to the same UNI isolated VLAN. Local switching is allowed among ports that belong to a UNI community VLAN. Because all ports on the ME 3800X and 3600X switches are NNIs, UNI VLAN configuration has no effect. Local switching is allowed between NNIs.

Switch Ports

Switch ports are Layer 2 only interfaces associated with a physical port. Switch ports belong to one or more VLANs. You can configure a port as an access port or trunk port. Switch ports are used for managing the physical interface and associated Layer 2 protocols and do not handle routing or bridging.

Configure switch ports by using the switchport interface configuration commands. Use the switchport command with no keywords to put an interface that is in Layer 3 mode into Layer 2 mode.

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Note When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.

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For detailed information about configuring access port and trunk port characteristics, see Chapter 11 "Configuring VLANs."

Access Ports

An access port belongs to and carries the traffic of only one VLAN. Traffic is received and sent in native formats with no VLAN tagging. Traffic arriving on an access port is assumed to belong to the VLAN assigned to the port. If an access port receives an IEEE 802.1Q tagged packet, the packet is dropped, and the source address is not learned. IEEE 802.1x can also be used for VLAN assignment.

You manually assign static access ports to a VLAN.

Trunk Ports

An IEEE 802.1Q trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN database. A trunk port supports simultaneous tagged and untagged traffic. An IEEE 802.1Q trunk port is assigned a default Port VLAN ID (PVID), and all untagged traffic travels on the port default PVID. All untagged traffic and tagged traffic with a NULL VLAN ID are assumed to belong to the port default PVID. A packet with a VLAN ID equal to the outgoing port default PVID is sent untagged. All other traffic is sent with a VLAN tag.

Although by default a trunk port is a member of multiple VLANs, you can limit VLAN membership by configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs does not affect any other port but the associated trunk port. By default, all possible VLANs (VLAN ID 1 to 4094) are in the allowed list. A trunk port can become a member of a VLAN only if the VLAN is in the enabled state.

For more information about trunk ports, see Chapter 11 "Configuring VLANs."

Routed Ports

A routed port is a physical port that acts like a port on a router; it does not have to be connected to a router. A routed port is not associated with a particular VLAN, as is an access port. A routed port behaves like a regular router interface, except that it does not support VLAN subinterfaces. Routed ports can be configured with a Layer 3 routing protocol. A routed port is a Layer 3 interface only and does not support Layer 2 protocols, such as STP.

Configure routed ports by putting the interface into Layer 3 mode with the no switchport interface configuration command. Then assign an IP address to the port, enable routing, and assign routing protocol characteristics by using the ip routing and router protocol global configuration commands.

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Note Entering a no switchport interface configuration command shuts down the interface and then re-enables it, which might generate messages on the device to which the interface is connected. When you put an interface that is in Layer 2 mode into Layer 3 mode, the previous configuration information related to the affected interface might be lost.

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The number of routed ports that you can configure is not limited by software. However, the interrelationship between this number and the number of other features being configured might impact CPU performance because of hardware limitations. See the "Configuring Layer 3 Interfaces" section for information about what happens when hardware resource limitations are reached.

For more information about IP unicast and multicast routing and routing protocols, see Chapter 36 "Configuring IP Unicast Routing" and Chapter 43 "Configuring IP Multicast Routing."

Ethernet Management Port

The Ethernet management port, also referred to as the Gi0 or gigabitethernet0 port, is a Layer 3 host port to which you can connect a PC. You can use the Ethernet management port instead of the switch console port for network management.

See the "Using the Ethernet Management Port" section for more information.

Switch Virtual Interfaces

A switch virtual interface (SVI) represents a VLAN of switch ports as one interface to the routing or bridging function in the system. Only one SVI can be associated with a VLAN, but you need to configure an SVI for a VLAN only when you wish to route between VLANs or to provide IP host connectivity to the switch. By default, an SVI is created for the default VLAN (VLAN 1) to permit remote switch administration. Additional SVIs must be explicitly configured.

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Note You cannot delete interface VLAN 1.

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SVIs provide IP host connectivity only to the system; in Layer 3 mode, you can configure routing across SVIs.

Although the switch supports a total of 1005 VLANs (and SVIs), the interrelationship between the number of SVIs and routed ports and the number of other features being configured might impact CPU performance because of hardware limitations. See the "Configuring Layer 3 Interfaces" section for information about what happens when hardware resource limitations are reached.

SVIs are created the first time that you enter the vlan interface configuration command for a VLAN interface. The VLAN corresponds to the VLAN tag associated with data frames on an IEEE 802.1Q encapsulated trunk or the VLAN ID configured for an access port. Configure a VLAN interface for each VLAN for which you want to route traffic, and assign it an IP address. For more information, see the "Manually Assigning IP Information" section.

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Note When you create an SVI, it does not become active until it is associated with a physical port.

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SVIs support routing protocols. For more information about configuring IP routing, see Chapter 36 "Configuring IP Unicast Routing," and Chapter 43 "Configuring IP Multicast Routing."

EtherChannel Port Groups

EtherChannel port groups treat multiple switch ports as one switch port. These port groups act as a single logical port for high-bandwidth connections between switches or between switches and servers. An EtherChannel balances the traffic load across the links in the channel. If a link within the EtherChannel fails, traffic previously carried over the failed link changes to the remaining links. You can group multiple trunk ports into one logical trunk port, group multiple access ports into one logical access port, or group multiple routed ports into one logical routed port. Most protocols operate over either single ports or aggregated switch ports and do not recognize the physical ports within the port group. Exceptions are the Cisco Discovery Protocol (CDP), Link Aggregation Control Protocol (LACP), and the Port Aggregation Protocol (PAgP), which operate only on physical NNI or ENI ports.

When you configure an EtherChannel, you create a port-channel logical interface and assign an interface to the EtherChannel. For Layer 3 interfaces, you manually create the logical interface by using the interface port-channel global configuration command. Then you manually assign an interface to the EtherChannel by using the channel-group interface configuration command. For Layer 2 interfaces, use the channel-group interface configuration command to dynamically create the port-channel logical interface. This command binds the physical and logical ports together. For more information, see Chapter 35 "Configuring EtherChannels."

Ethernet Flow Points

An Ethernet Flow Point (EFP) is a logical interface that connects an Ethernet Virtual Connection (EVC) bridge domain to a physical port in a switch. Configuring a service instance on an interface creates a pseudoport or EFP on which you configure EVC features.

You can configure EFP service instances only on Layer 2 ports. You can configure an EtherChannel with a service instance, but you cannot add an interface to a channel group if it has a service instance configured on it. EFPs do not support routing. EFPs do not support switchport commands.

Switch interfaces configured with service instances support a different range of features than interfaces that do not have service instances. For more information on EVCs, see Chapter 12 "Configuring Ethernet Virtual Connections (EVCs)."

Connecting Interfaces

Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs cannot exchange data without going through a routing device. With a standard Layer 2 switch, ports in different VLANs have to exchange information through a router. By using the switch with routing enabled, when you configure both VLAN 20 and VLAN 30 with an SVI to which an IP address is assigned, packets can be sent from Host A to Host B directly through the switch with no need for an external router (Figure 10-1).

Figure 10-1 Connecting VLANs with the Switch

You can enable routing on all SVIs and routed ports on the switch. Whenever possible, to maintain high performance, forwarding is done by the switch hardware. However, only IP Version 4 packets with Ethernet II encapsulation can be routed in hardware. The switch routes only IP traffic. When IP routing protocol parameters and address configuration are added to an SVI or routed port, any IP traffic received from these ports is routed. For more information, see Chapter 36 "Configuring IP Unicast Routing" and Chapter 43 "Configuring IP Multicast Routing."

Using Interface Configuration Mode

The switch supports these interface types:

•Physical ports—switch ports, routed ports

•SVIs—switch virtual interfaces

•Port-channels—EtherChannel interfaces

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Note The switch also supports EFP service instances configured on physical interfaces. You configure EFPs in service-instance configuration mode. See Chapter 12 "Configuring Ethernet Virtual Connections (EVCs)."

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You can also configure a range of interfaces (see the "Configuring a Range of Interfaces" section).

To configure a physical interface (port), specify the interface type, the module number, and the switch port number, and enter interface configuration mode.

•Type—Gigabit Ethernet (gigabitethernet or gi) for 10/100/1000 Mb/s Ethernet ports, or small form-factor pluggable (SFP) module Gigabit Ethernet interfaces.

•Module number—The module or slot number on the switch (always 0 on the Cisco ME switch).

•Port number—The interface number on the switch. The port numbers always begin at 1, starting with the leftmost port when facing the front of the switch, for example, gigabitethernet 0/1. If there is more than one interface type (for example, 10/100/1000 ports and SFP module ports), the port numbers restart with the second interface type: gigabitethernet 0/1.

You can identify physical interfaces by physically checking the interface location on the switch. You can also use the show privileged EXEC commands to display information about a specific interface or all the interfaces on the switch. The remainder of this chapter primarily provides physical interface configuration procedures.

Procedures for Configuring Interfaces

These general instructions apply to all interface configuration processes.

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Step 1 Enter the configure terminal command at the privileged EXEC prompt:

Switch# configure terminal 

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# 

Step 2 Enter the interface global configuration command. Identify the interface type and the number of the connector. In this example, Fast Ethernet port 1 is selected:

Switch(config)# interface gigabitethernet0/1 

Switch(config-if)# 

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Note You do not need to add a space between the interface type and interface number. For example, in the preceding line, you can specify either gigabitethernet 0/1, gigabitethernet0/1, gi 0/1, or gi0/1.

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Step 3 Follow each interface command with the interface configuration commands that the interface requires. The commands that you enter define the protocols and applications that will run on the interface. The commands are collected and applied to the interface when you enter another interface command or enter end to return to privileged EXEC mode.

You can also configure a range of interfaces by using the interface range or interface range macro global configuration commands. Interfaces configured in a range must be the same type and must be configured with the same feature options.

Step 4 After you configure an interface, verify its status by using the show privileged EXEC commands listed in the "Monitoring and Maintaining the Interfaces" section.

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Enter the show interfaces privileged EXEC command to see a list of all interfaces on or configured for the switch. A report is provided for each interface that the device supports or for the specified interface.

Configuring a Range of Interfaces

You can use the interface range global configuration command to configure multiple interfaces with the same configuration parameters. When you enter the interface range configuration mode, all command parameters that you enter are attributed to all interfaces within that range until you exit this mode.

Beginning in privileged EXEC mode, follow these steps to configure a range of interfaces with the same parameters:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface range {port-range}	Specify the range of interfaces (VLANs or physical ports) to be configured, and enter interface range configuration mode. •You can use the interface range command to configure up to five port ranges or a previously defined macro. •In a comma-separated port-range, you must enter the interface type for each entry and enter spaces before and after the comma. •In a hyphen-separated port-range, you do not need to re-enter the interface type, but you must enter a space before the hyphen.
Step 3		You can now use the normal configuration commands to apply the configuration parameters to all interfaces in the range.
Step 4	end	Return to privileged EXEC mode.
Step 5	show interfaces [interface-id]	Verify the configuration of the interfaces in the range.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

When using the interface range global configuration command, note these guidelines:

•Valid entries for port-range:

–vlan vlan-ID - vlan-ID, where the VLAN ID is 1 to 4094

–gigabitethernet module/{first port} - {last port}, where the module is always 0

–tengigabitethernet module/{first port} - {last port}, where the module is always 0

–port-channel port-channel-number - port-channel-number, where the port-channel-number is 1 to 26

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Note When you use the interface range command with port channels, the first and last port channel number must be active port channels.

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•The interface range command only works with VLAN interfaces that have been configured with the interface vlan command. The show running-config privileged EXEC command displays the configured VLAN interfaces. VLAN interfaces not displayed by the show running-config command cannot be used with the interface range command.

•All interfaces defined as in a range must be the same type (all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or all VLANs), but you can enter multiple ranges in a command.

This example shows how to use the interface range global configuration command to set the speed on ports 1 and 2 to 100 Mb/s:

Switch# configure terminal

Switch(config)# interface range gigabitethernet0/1 - 2

Switch(config-if-range)# speed 100

This example shows how to use a comma to add different interface type strings to the range to enable Fast Ethernet ports 1 to 3 and Gigabit Ethernet ports 1 and 2 to receive IEEE 802.3x flow control pause frames:

Switch# configure terminal

Switch(config)# interface range gigabitethernet0/1 - 3 , gigabitethernet0/5 - 6 

Switch(config-if-range)# flowcontrol receive on

If you enter multiple configuration commands while you are in interface range mode, each command is executed as it is entered. The commands are not batched together and executed after you exit interface range mode. If you exit interface range configuration mode while the commands are being executed, some commands might not be executed on all interfaces in the range. Wait until the command prompt reappears before exiting interface range configuration mode.

Configuring and Using Interface Range Macros

You can create an interface range macro to automatically select a range of interfaces for configuration. Before you can use the macro keyword in the interface range macro global configuration command string, you must use the define interface-range global configuration command to define the macro.

Beginning in privileged EXEC mode, follow these steps to define an interface range macro:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	define interface-range macro_name interface-range	Define the interface-range macro, and save it in NVRAM. •The macro_name is a 32-character maximum character string. •A macro can contain up to five comma-separated interface ranges. •Each interface-range must consist of the same port type.
Step 3	interface range macro macro_name	Select the interface range to be configured using the values saved in the interface-range macro called macro_name. You can now use the normal configuration commands to apply the configuration to all interfaces in the defined macro.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config | include define	Show the defined interface range macro configuration.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Use the no define interface-range macro_name global configuration command to delete a macro.

When using the define interface-range global configuration command, note these guidelines:

•Valid entries for interface-range:

–vlan vlan-ID - vlan-ID, where the VLAN ID is 1 to 4094

–gigabitethernet module/{first port} - {last port}, where the module is always 0

–tengigabitethernet module/{first port} - {last port}, where the module is always 0

–port-channel port-channel-number - port-channel-number, where the port-channel-number is 1 to 26.

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Note When you use the interface ranges with port channels, the first and last port channel number must be active port channels.

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•You must add a space between the first interface number and the hyphen when entering an interface-range. For example, gigabitethernet0/1 - 2 is a valid range; gigabitethernet0/1-2 is not a valid range.

•The VLAN interfaces must have been configured with the interface vlan command. The show running-config privileged EXEC command displays the configured VLAN interfaces. VLAN interfaces not displayed by the show running-config command cannot be used as interface-ranges.

•All interfaces defined as in a range must be the same type (all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or all VLANs), but you can combine multiple interface types in a macro.

This example shows how to define an interface-range named enet_list to include ports 1 and 2 and to verify the macro configuration:

Switch# configure terminal

Switch(config)# define interface-range enet_list gigabitethernet0/1 - 2

Switch(config)# end

Switch# show running-config | include define 

define interface-range enet_list GigabitEthernet0/1 - 2

This example shows how to create a multiple-interface macro named macro1 and assign all of the interfaces in the range to a VLAN:

Switch# configure terminal

Switch(config)# define interface-range macro1 gigabitethernet0/1 - 2, gigabitethernet0/5 - 
6

Switch(config)# interface range macro macro1

Switch(config-if-range)# switchport access vlan 20

Switch(config-if-range)# end

This example shows how to enter interface range configuration mode for the interface-range macro enet_list:

Switch# configure terminal

Switch(config)# interface range macro enet_list 

Switch(config-if-range)# 

This example shows how to delete the interface-range macro enet_list and to verify that it was deleted.

Switch# configure terminal

Switch(config)# no define interface-range enet_list 

Switch(config)# end

Switch# show run | include define

Switch# 

Using the Ethernet Management Port

•Understanding the Ethernet Management Port

•Supported Features on the Ethernet Management Port

•Configuring the Ethernet Management Port

•TFTP and the Ethernet Management Port

Understanding the Ethernet Management Port

The Ethernet management port is port Gi0 or gigabitethernet0, a Layer 3 host port to which you can connect a PC. You can use the Ethernet management port instead of the switch console port for network management.

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Note You cannot configure an EFP service instance on the Ethernet management port.

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When connecting a PC to the Ethernet management port, you must assign an IP address. Connect the Ethernet management port to the PC as shown in Figure 10-2.

Figure 10-2 Connecting a Switch to a PC

By default, the Ethernet management port is enabled. The switch cannot route packets from the Ethernet management port to a network port or receive routed packets from a network port.

Even though the Ethernet management port does not support routing, you might need to enable routing protocols on the port. For example, in Figure 10-3, you must enable routing protocols on the Ethernet management port when the PC is two or more hops away from the switch and the packets must pass through two or more Layer 3 devices to reach the PC.

Figure 10-3 Network Example with Routing Protocols Enabled

In Figure 10-3, if the Ethernet management port and the network ports are associated with the same routing process, the routes are propagated in this manner:

•The routes from the Ethernet management port are propagated through the network ports to the network.

•The routes from the network ports are propagated through the Ethernet management port to the network.

Because routing is not supported between the Ethernet management port and the network ports, traffic cannot be sent or received between these ports. If traffic is sent or received, data packet loops occur between the ports, which disrupts the switch and network operation. Configure route filters to avoid routes between the Ethernet management port and the network ports and to prevent the loops.

Supported Features on the Ethernet Management Port

The Ethernet management port supports these features:

•Telnet with passwords

•TFTP

•Secure Shell (SSH)

•DHCP-based autoconfiguration

•SMNP (only the ENTITY-MIB and the IF-MIB)

•IP ping

•Interface features

•Speed—1000 Mb/s, and autonegotiation

•Duplex mode—Full, half, and autonegotiation

•Loopback detection

•Cisco Discovery Protocol (CDP)

•DHCP relay agent

•IPv4 access control lists (ACLs)

•Routing protocols

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Caution Before enabling a feature on the Ethernet management port, make sure that the feature is supported. If you try to configure an unsupported feature on the Ethernet Management port, the feature might not work properly, and the switch might fail.

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Configuring the Ethernet Management Port

To specify the Ethernet management port in the CLI, enter gigabitethernet0.

To disable the port, use the shutdown interface configuration command. To enable the port, use the no shutdown interface configuration command.

You can monitor the Ethernet management port LED to determine the link status to the PC. The LED is green (on) when the link is active, and the LED is off when the link is down. The LED is amber when there is a POST failure.

To display the link status, use the show interfaces gigabitethernet 0 privileged EXEC command.

TFTP and the Ethernet Management Port

Use the commands in Table 1 when using TFTP to download or upload a configuration file to the boot loader.

Table 1 Boot Loader Commands 

Command	Description
arp [ip_address]	Displays the currently cached ARP1 table when this command is entered without the ip_address parameter. Enables ARP to associate a MAC address with the specified IP address when this command is entered with the ip_address parameter.
mgmt_clr	Clears the statistics for the Ethernet management port.
mgmt_init	Starts the Ethernet management port.
mgmt_show	Displays the statistics for the Ethernet management port.
ping host_ip_address	Sends ICMP ECHO_REQUEST packets to the specified network host.
boot tftp:/file-url ...	Loads and boots an executable image from the TFTP server and enters the command-line interface. For more details, see the command reference for this release.
copy tftp:/source-file-url filesystem:/destination-file-url	Copies a Cisco IOS image from the TFTP server to the specified location. For more details, see the command reference for this release.

1 ARP = Address Resolution Protocol.

Configuring Ethernet Interfaces

•Default Ethernet Interface Configuration

•Configuring Interface Speed and Duplex Mode

•Configuring IEEE 802.3x Flow Control

•Configuring Auto-MDIX on an Interface

•Adding a Description for an Interface

Default Ethernet Interface Configuration

Table 10-2 shows the Ethernet interface default configuration. For more details on the VLAN parameters listed in the table, see Chapter 11 "Configuring VLANs." For details on controlling traffic to the port, see Chapter 23 "Configuring Traffic Control."

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Note To configure Layer 2 parameters, if the interface is in Layer 3 mode, you must enter the switchport interface configuration command without any parameters to put the interface into Layer 2 mode. This shuts down the interface and then re-enables it, which might generate messages on the device to which the interface is connected. When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.

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Table 10-2 Default Ethernet Configuration

Feature	Default Setting
Operating mode	Layer 2 or switching mode (switchport command).
Allowed VLAN range	VLANs 1- 4094.
Default VLAN (for access ports)	VLAN 1 (Layer 2 interfaces only).
Native VLAN (for IEEE 802.1Q trunks)	VLAN 1 (Layer 2 interfaces only).
VLAN trunking	Switchport mode access (Layer 2 interfaces only).
Port enable state	Enabled.
Port description	None defined.
Speed	Autonegotiate.
Duplex mode	Autonegotiate.
IEEE 802.3x flow control	Flow control is set to receive: off. It is always off for sent packets.
EtherChannel	Disabled on all Ethernet ports. See Chapter 35 "Configuring EtherChannels."
Broadcast, multicast, and unicast storm control	Disabled. See the "Default Storm Control Configuration" section.
Port Fast	Disabled. See the "Default Optional Spanning-Tree Configuration" section.
Auto-MDIX	Enabled.
Cisco Discovery Protocol (CDP)	Enabled.

Configuring Interface Speed and Duplex Mode

Ethernet interfaces on the switch operate at 10, 100, or 1000 Mb/s or and in either full- or half-duplex mode. In full-duplex mode, two stations can send and receive traffic at the same time. Normally, 10-Mb/s ports operate in half-duplex mode, which means that stations can either receive or send traffic.

Switch models include combinations Gigabit Ethernet (10/100/1000-Mb/s) ports and small form-factor pluggable (SFP) module slots supporting SFP modules.

•Speed and Duplex Configuration Guidelines

•Setting the Interface Speed and Duplex Parameters

Speed and Duplex Configuration Guidelines

When configuring an interface speed and duplex mode, note these guidelines:

•You can configure interface speed on Gigabit Ethernet (10/100/1000-Mb/s) ports. You can configure Gigabit Ethernet ports to full-duplex mode or to autonegotiate. You also can configure Gigabit Ethernet ports to half-duplex mode if the speed is 10 or 100 Mb/s. Half-duplex mode is not supported on Gigabit Ethernet ports operating at 1000 Mb/s.

•You cannot configure speed on a 1g SFP or 10g SFP+ port. You can configure speed to not negotiate (nonegotiate) on 1g SFP ports only, if they are connected to a device that does not support autonegotiation. Speed nonegotiate is not supported on the 10g SFP+ interfaces.

The exception is when a 1000BASE-T SFP module is in the SFP module slot, you can configure speed as 10, 100, or 1000 Mb/s, or auto, but not as nonegotiate.

On a 100BASE-FX SFP module, you cannot configure the speed as nonegotiate.

•You cannot configure duplex mode on 10 GigabitEthernet ports. The duplex command is not available.

•You cannot configure duplex mode on SFP module ports; they operate in full-duplex mode except in these situations:

–When a Cisco1000BASE-T SFP module is in the SFP module slot, you can configure duplex mode to auto or full. Half-duplex mode is supported with the auto setting.

–When a Cisco100BASE-FX SFP module is in the SFP module slot, you can configure duplex mode to half or full. Although the auto keyword is available, it puts the interface in half-duplex mode (the default for this SFP module) because the 100BASE-FX SFP module does not support autonegotiation.

•If both ends of the line support autonegotiation, we highly recommend the default setting of auto negotiation.

•If one interface supports autonegotiation and the other end does not, configure duplex and speed on both interfaces; do not use the auto setting on the supported side.

•When STP is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for loops. The port LED is amber while STP reconfigures.

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Caution Changing the interface speed and duplex mode configuration might shut down and re-enable the interface during the reconfiguration.

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Setting the Interface Speed and Duplex Parameters

Beginning in privileged EXEC mode, follow these steps to set the speed and duplex mode for a physical interface.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Specify the physical interface to be configured, and enter interface configuration mode.
Step 3	speed {10 | 100 | 1000 | auto [10 | 100 | 1000] | nonegotiate}	Enter the appropriate speed parameter for the interface: •Enter 10, 100, or 1000 to set a specific speed for the interface. The 1000 keyword is available only for 10/100/1000 Mb/s ports or SFP module ports with a 1000BASE-T SFP module. •Enter auto to enable the interface to autonegotiate speed with the connected device. If you use the 10, 100, or the 1000 keywords with the auto keyword, the port autonegotiates only at the specified speeds. •The nonegotiate keyword is available but not supported. When a Cisco1000BASE-T SFP module is in the SFP module slot, the speed can be configured to 10, 100, 1000, or to auto, but not to nonegotiate.
Step 4	duplex {auto | full | half}	Enter the duplex parameter for the interface. Enable half-duplex mode (for interfaces operating only at 10 or 100 Mb/s). You cannot configure half-duplex mode for interfaces operating at 1000 Mb/s. You can configure the duplex setting when the speed is set to auto. This command is not available on 10 GigabitEthernet ports or on SFP module ports with these exceptions: •If a Cisco 1000BASE-T SFP module is inserted, you can configure duplex to auto or to full. •If a Cisco 100BASE-FX SFP module is inserted, you can configure duplex to full or to half. Although the auto keyword is available, it puts the interface in half-duplex mode (the default).
Step 5	end	Return to privileged EXEC mode.
Step 6	show interfaces interface-id	Display the interface speed and duplex mode configuration.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Use the no speed and no duplex interface configuration commands to return the interface to the default speed and duplex settings (autonegotiate). To return all interface settings to the defaults, use the default interface interface-id interface configuration command.

This example shows how to set the interface speed to 10 Mb/s and the duplex mode to half:

Switch# configure terminal

Switch(config)# interface gigabitethernet0/3

Switch(config-if)# speed 10

Switch(config-if)# duplex half

This example shows how to set the interface speed to 100 Mb/s on a 10/100/1000 Mb/s port:

Switch# configure terminal

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# speed 100

Configuring IEEE 802.3x Flow Control

IEEE 802.3x flow control enables connected Ethernet ports to control traffic rates during congestion by allowing congested nodes to pause link operation at the other end. If one port experiences congestion and cannot receive any more traffic, it notifies the other port by sending a pause frame to stop sending until the condition clears. Upon receipt of a pause frame, the sending device stops sending any data packets, which prevents any loss of data packets during the congestion period.

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Note Ports can receive, but not send, pause frames.

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You use the flowcontrol interface configuration command to set the interface's ability to receive pause frames to on, off, or desired. The default state is off.

When set to desired, an interface can operate with an attached device that is required to send flow-control packets or with an attached device that is not required to but can send flow-control packets.

These rules apply to IEEE 802.3x flow control settings on the device:

•receive on (or desired): The port cannot send pause frames but can operate with an attached device that is required to or can send pause frames; the port can receive pause frames.

•receive off: IEEE 802.3x flow control does not operate in either direction. In case of congestion, no indication is given to the link partner, and no pause frames are sent or received by either device.

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Note For details on the command settings and the resulting IEEE 802.3x flow control resolution on local and remote ports, see the flowcontrol interface configuration command in the command reference for this release.

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Beginning in privileged EXEC mode, follow these steps to configure IEEE 802.3x flow control on an interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode
Step 2	interface interface-id	Specify the physical interface to be configured, and enter interface configuration mode.
Step 3	flowcontrol {receive} {on | off | desired}	Configure the IEEE 802.3x flow control mode for the port.
Step 4	end	Return to privileged EXEC mode.
Step 5	show interfaces interface-id	Verify the interface IEEE 802.3x flow control settings.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable IEEE 802.3x flow control, use the flowcontrol receive off interface configuration command.

This example shows how to enable IEEE 802.3x flow control on a port:

Switch# configure terminal

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# flowcontrol receive on

Switch(config-if)# end

Configuring Auto-MDIX on an Interface

When automatic medium-dependent interface crossover (auto-MDIX) is enabled on an interface, the interface automatically detects the required cable connection type (straight through or crossover) and configures the connection appropriately. When connecting switches without the auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters. With auto-MDIX enabled, you can use either type of cable to connect to other devices, and the interface automatically corrects for any incorrect cabling. For more information about cabling requirements, see the hardware installation guide.

Auto-MDIX is enabled by default. When you enable auto-MDIX, you must also set the speed and duplex on the interface to auto so that the feature operates correctly. Auto-MDIX is supported on all 10/100 and 10/100/1000 Mb/s interfaces and on Cisco 10/100/1000 BASE-T/TX SFP module interfaces. It is not supported on 1000 BASE-SX or -LX SFP module interfaces.

Table 10-3 shows the link states that result from auto-MDIX settings and correct and incorrect cabling.

Table 10-3 Link Conditions and Auto-MDIX Settings 

Local Side Auto-MDIX	Remote Side Auto-MDIX	With Correct Cabling	With Incorrect Cabling
On	On	Link up	Link up
On	Off	Link up	Link up
Off	On	Link up	Link up
Off	Off	Link up	Link down

Beginning in privileged EXEC mode, follow these steps to configure auto-MDIX on an interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode
Step 2	interface interface-id	Specify the physical interface to be configured, and enter interface configuration mode.
Step 3	speed auto	Configure the interface to autonegotiate speed with the connected device.
Step 4	duplex auto	Configure the interface to autonegotiate duplex mode with the connected device.
Step 5	mdix auto	Enable auto-MDIX on the interface.
Step 6	end	Return to privileged EXEC mode.
Step 7	show controllers ethernet-controller interface-id phy	Verify the operational state of the auto-MDIX feature on the interface. Command is there, but no mdix in output.
Step 8	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable auto-MDIX, use the no mdix auto interface configuration command.

This example shows how to enable auto-MDIX on a port:

Switch# configure terminal

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# speed auto

Switch(config-if)# duplex auto

Switch(config-if)# mdix auto

Switch(config-if)# end

Adding a Description for an Interface

You can add a description about an interface to help you remember its function. The description appears in the output of these privileged EXEC commands: show configuration, show running-config, and show interfaces.

Beginning in privileged EXEC mode, follow these steps to add a description for an interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Specify the interface for which you are adding a description, and enter interface configuration mode.
Step 3	description string	Add a description (up to 240 characters) for an interface.
Step 4	end	Return to privileged EXEC mode.
Step 5	show interfaces interface-id description or show running-config	Verify your entry.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Use the no description interface configuration command to delete the description.

This example shows how to add a description on a port and how to verify the description:

Switch# config terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# description Connects to Marketing

Switch(config-if)# end

Switch# show interfaces gigabitethernet0/2 description

Interface Status         Protocol Description

Gi 0/2   admin down     down     Connects to Marketing

Configuring Layer 3 Interfaces

The switch supports these types of Layer 3 interfaces:

•SVIs: You should configure SVIs for any VLANs for which you want to route traffic. SVIs are created when you enter a VLAN ID following the interface vlan global configuration command. To delete an SVI, use the no interface vlan global configuration command. You cannot delete interface VLAN 1.

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Note When you create an SVI, it does not become active until it is associated with a physical port. For information about assigning Layer 2 ports to VLANs, see Chapter 11 "Configuring VLANs."

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•Routed ports: Routed ports are physical ports configured to be in Layer 3 mode by using the no switchport interface configuration command.

•Layer 3 EtherChannel ports: EtherChannel interfaces made up of routed ports.

EtherChannel port interfaces are described in Chapter 35 "Configuring EtherChannels."

A Layer 3 switch can have an IP address assigned to each routed port and SVI.

There is no defined limit to the number of SVIs and routed ports that can be configured in a switch. However, the interrelationship between the number of SVIs and routed ports and the number of other features being configured might have an impact on CPU usage because of hardware limitations. If the switch is using maximum hardware resources, attempts to create a routed port or SVI have these results:

•If you try to create a new routed port, the switch generates a message that there are not enough resources to convert the interface to a routed port, and the interface remains as a switch port.

•If you try to create an extended-range VLAN, an error message is generated, and the extended-range VLAN is rejected.

•If the switch attempts to boot up with a configuration that has more VLANs and routed ports than hardware can support, the VLANs are created, but the routed ports are shut down, and the switch sends a message that this was due to insufficient hardware resources.

All Layer 3 interfaces require an IP address to route traffic. This procedure shows how to configure an interface as a Layer 3 interface and how to assign an IP address to an interface.

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Note If the physical port is in Layer 2 mode (the default), you must enter the no switchport interface configuration command to put the interface into Layer 3 mode. Entering a no switchport command disables and then re-enables the interface, which might generate messages on the device to which the interface is connected. Furthermore, when you put an interface that is in Layer 2 mode into Layer 3 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration

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Beginning in privileged EXEC mode, follow these steps to configure a Layer 3 interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface {gigabitethernet} interface-id} | {vlan vlan-id} | {port-channel port-channel-number}	Specify the interface to be configured as a Layer 3 interface, and enter interface configuration mode.
Step 3	no switchport	For physical ports only, enter Layer 3 mode.
Step 4	ip address ip_address subnet_mask	Configure the IP address and IP subnet.
Step 5	end	Return to privileged EXEC mode.
Step 6	show interfaces [interface-id] show ip interface [interface-id] show running-config interface [interface-id]	Verify the configuration.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove an IP address from an interface, use the no ip address interface configuration command.

This example shows how to configure a port as a routed port and to assign it an IP address:

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# no switchport

Switch(config-if)# ip address 192.20.135.21 255.255.255.0

Configuring the Interface MTU

You can configure the maximum transmission unit (MTU) size on an interface to determine the packet size that can be received on the interface. Because the switch does not fragment Layer 2 packets, it drops switched Layer 2 packets larger than the packet size supported on the egress interface.

Beginning in privileged EXEC mode, follow these steps to change the MTU size on an interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Specify the interface to be configured, and enter interface configuration mode. The interface must be a physical interface, but it can be one on which a service instance is configured.
Step 3	mtu bytes	Configure the MTU size for the interface. The range is from 1500 to 9800 bytes. The default is 1500.
Step 4	end	Return to privileged EXEC mode.
Step 5	show interface interface-id	Verify the configuration.
Step 6	copy running-config startup-config	Save your entries in the configuration file.

This example shows how to set the maximum packet size for a Gigabit Ethernet port to 1800 bytes:

Switch(config)# interface gigabitethernet0/3

Switch(config-if)# mtu 1800

Switch(config)# exit

Monitoring and Maintaining the Interfaces

These sections contain interface monitoring and maintenance information:

•Monitoring Interface Status

•Clearing and Resetting Interfaces and Counters

•Shutting Down and Restarting the Interface

Monitoring Interface Status

Commands entered at the privileged EXEC prompt display information about the interface, including the versions of the software and the hardware, the configuration, and statistics about the interfaces. Table 10-4 lists some of these interface monitoring commands. (You can display the full list of show commands by using the show ? command at the privileged EXEC prompt.) These commands are fully described in the Cisco IOS Interface Command Reference, Release 12.2.

Table 10-4 Show Commands for Interfaces 

Command	Purpose
show interfaces [interface-id]	Display the status and configuration of all interfaces or a specific interface.
show interfaces interface-id status [err-disabled]	Display interface status or a list of interfaces in an error-disabled state.
show interfaces [interface-id] switchport	Display administrative and operational status of switching mode. You can use this command to find out if a port is in routing or in switching mode.
show interfaces [interface-id] description	Display the description configured on an interface or all interfaces and the interface status.
show ip interface [interface-id]	Display the usability status of all interfaces configured for IP routing or the specified interface.
show interface [interface-id] stats	Display the input and output packets by the switching path for the interface.
show interfaces [interface-id] transceiver [detail | dom-supported-list | module number | properties | threshold-table]	Display these physical and operational status about an SFP module: •interface-id-(Optional) Display configuration and status for a specified physical interface. •detail-(Optional) Display calibration properties, including high and low numbers and any alarm information for any Digital Optical Monitoring (DoM)-capable transceiver if one is installed in the switch. •dom-supported-list-(Optional) List all supported DoM transceivers. •module number-(Optional) Limit display to interfaces on module on the switch. The range is 1 to 9. This option is not available if you entered a specific interface ID. •properties-(Optional) Display speed, duplex, and inline power settings on an interface •threshold-table-(Optional) Display alarm and warning threshold table Note DoM monitoring is by default set to On. To turn Off set the configuration to: transceiver type all no monitoring.
show port-type [eni | nni | uni]	Display interface type information for the Cisco ME switch. The only valid type is nni. Other keywords show no output.
show running-config interface [interface-id]	Display the running configuration in RAM for the interface.
show version	Display the hardware configuration, software version, the names and sources of configuration files, and the boot images.
show controllers ethernet-controller interface-id phy	Display the operational state of the auto-MDIX feature on the interface.

Clearing and Resetting Interfaces and Counters

Table 10-5 lists the privileged EXEC mode clear commands that you can use to clear counters and reset interfaces.

Table 10-5 Clear Commands for Interfaces 

Command	Purpose
clear counters [interface-id]	Clear interface counters.
clear interface interface-id	Reset the hardware logic on an interface.
clear line [number | console 0 | vty number]	Reset the hardware logic on an asynchronous serial line.

To clear the interface counters shown by the show interfaces privileged EXEC command, use the clear counters privileged EXEC command. The clear counters command clears all current interface counters from the interface unless you specify optional arguments that clear only a specific interface type from a specific interface number.

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Note The clear counters privileged EXEC command does not clear counters retrieved by using Simple Network Management Protocol (SNMP), but only those seen with the show interface privileged EXEC command.

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Shutting Down and Restarting the Interface

Shutting down an interface disables all functions on the specified interface and marks 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 mentioned in any routing updates.

Beginning in privileged EXEC mode, follow these steps to shut down an interface:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface {vlan vlan-id} | {gigabitethernet interface-id} | {port-channel port-channel-number}	Select the interface to be configured.
Step 3	shutdown	Shut down an interface.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config	Verify your entry.

Use the no shutdown interface configuration command to enable an interface.

To verify that an interface is disabled, enter the show interfaces privileged EXEC command. A disabled interface is shown as administratively down in the display.