This section describes the different types of interfaces supported by the switch. The rest of the chapter describes configuration procedures for physical interface characteristics.

Note	The stack ports on the rear of the stacking-capable switches are not Ethernet ports and cannot be configured.

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.

When the IP Services image is running on the switch or the active switch, the switch uses two methods to forward traffic between interfaces: routing and fallback bridging. If the IP Base image is on the switch or the active switch, only basic routing (static routing and RIP) is supported. Whenever possible, to maintain high performance, forwarding is done by the switch hardware. However, only IPv4 packets with Ethernet II encapsulation are routed in hardware. Non-IP traffic and traffic with other encapsulation methods are fallback-bridged by hardware.

• The routing function can be enabled on all SVIs and routed ports. 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.

• Fallback bridging forwards traffic that the switch does not route or traffic belonging to a nonroutable protocol, such as DECnet. Fallback bridging connects multiple VLANs into one bridge domain by bridging between two or more SVIs or routed ports. When configuring fallback bridging, you assign SVIs or routed ports to bridge groups with each SVI or routed port assigned to only one bridge group. All interfaces in the same group belong to the same bridge domain.

The switch supports these interface types:

• Physical ports—switch ports and routed ports

• VLANs—switch virtual interfaces

• Port channels—EtherChannel interfaces

You can also configure a range of interfaces.

To configure a physical interface (port), specify the interface type, stack member number (only stacking-capable switches), module number, and switch port number, and enter interface configuration mode.

• Type—Gigabit Ethernet (gigabitethernet or gi) for 10/100/1000 Mb/s Ethernet ports, 10-Gigabit Ethernet (tengigabitethernet or te) for 10,000 Mb/s, or small form-factor pluggable (SFP) module Gigabit Ethernet interfaces (gigabitethernet or gi).

• Stack member number—The number that identifies the switch within the stack. The switch number range is 1 to 9 and is assigned the first time the switch initializes. The default switch number, before it is integrated into a switch stack, is 1. When a switch has been assigned a stack member number, it keeps that number until another is assigned to it.

  You can use the switch port LEDs in Stack mode to identify the stack member number of a switch.

• Module number—The module or slot number on the switch: switch (downlink) ports are 0, and uplink ports are 1.

• Port number—The interface number on the switch. The 10/100/1000 port numbers always begin at 1, starting with the far left port when facing the front of the switch, for example, gigabitethernet1/0/1 or gigabitethernet1/0/8.

  On a switch with 10/100/1000 ports and Cisco TwinGig Converter Modules in the 10-GigabitEthernet module slots, the port numbers restart with the 10-Gigabit Ethernet ports:tengigabitethernet1/0/1

  On a switch with 10/100/1000 ports and Cisco dual SFP X2 converter modules in the 10-Gigabit Ethernet module slots, the SFP module ports are numbered consecutively following the 10/100/1000 interfaces. For example, if the switch has 24 10/100/1000 ports, the SFP module ports are gigabitethernet1/0/25 through gigabitethernet1/0/28.

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.

These are examples of how to identify interfaces on a stacking-capable switch:

• To configure 10/100/1000 port 4 on a standalone switch, enter this command:

  
  Switch(config)# interface gigabitethernet1/0/4
  
  

• To configure 10-Gigabit Ethernet port 1 on a standalone switch, enter this command:

  
  Switch(config)# interface tengigabitethernet1/0/1
  
  

• To configure 10-Gigabit Ethernet port on stack member 3, enter this command:

  
  Switch(config)# interface tengigabitethernet3/0/1
  
  

• To configure the first SFP module port on stack member 1 with 16 10/100/1000 ports, enter this command:

  
  Switch(config)# interface gigabitethernet1/0/25
  
  

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.

  • gigabitethernet stack member/module {first port} -{last port} , where the module is always 0.

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

  • tengigabitethernet stack member/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 48.

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

• You must add a space between the first interface number and the hyphen when using the interface range command. For example, the command interface range gigabitethernet1/0/1 - 4 is a valid range; the command interface range gigabitethernet1/0/1-4 is not a valid range.

• 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 in a range must be the same type (all Gigabit Ethernet ports, all 10-Gigabit Ethernet ports, all EtherChannel ports, or all VLANs), but you can enter multiple ranges in a command.

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 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.

Ethernet interfaces on the switch operate at 10, 100, 1000, or 10,000 Mb/s 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 Gigabit Ethernet (10/100/1000-Mb/s) ports, 10-Gigabit Ethernet ports, and small form-factor pluggable (SFP) module slots supporting SFP modules.

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

• The 10-Gigabit Ethernet ports do not support the speed and duplex features. These ports operate only at 10,000 Mb/s and in full-duplex mode.

• Gigabit Ethernet (10/100/1000-Mb/s) ports support all speed options and all duplex options (auto, half, and full). However, Gigabit Ethernet ports operating at 1000 Mb/s do not support half-duplex mode.

• For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:

  • The 1000BASE-x (where -x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support the nonegotiate keyword in the speed interface configuration command. Duplex options are not supported.

  • The 1000BASE-T SFP module ports support the same speed and duplex options as the 10/100/1000-Mb/s ports.

• 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.

• As best practice, we suggest configuring the speed and duplex options on a link to auto or to fixed on both the ends. If one side of the link is configured to auto and the other side is configured to fixed, the link will not be up and this is expected.

Caution

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

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.

This table shows the Ethernet interface default configuration, including some features that apply only to Layer 2 interfaces.

Note	Layer 3 interfaces are not supported on switches running the LAN Base image.

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.

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

  When configuring SVIs, you can also configure SVI autostate exclude on a port in the SVI to exclude that port from being included in determining SVI line-state status.

• 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.

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 or in a switch stack. 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 its 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 switchport.

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

• If the switch is notified by VLAN Trunking Protocol (VTP) of a new VLAN, it sends a message that there are not enough hardware resources available and shuts down the VLAN. The output of the show vlan user EXEC command shows the VLAN in a suspended state.

• 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.

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

The Cisco eXpandable Power System (XPS) 2200 is a standalone power system that you can connect to the stacking-capable or nonstacking-capable switches. The XPS 2200 can provide backup power to connected devices that experience a power supply failure or, in power stack, it can supply additional power to the power stack budget.

The XPS 2200 power ports and internal power supplies can operate in redundant power supply (RPS) mode or stack power (SP) mode. Stack-power mode is used only on stacking-capable switches in a power stack. With no XPS, a power stack operates in ring topology with a maximum of four switches in the stack. If you merge two stacks, the total number of switches cannot exceed four. When an XPS is in the power stack, you can connect up to nine switches in the stack plus the XPS, providing power budgets to power stack members similar to stack-power ring topology operation.

All stacking-capable switches connected to an XPS on SP ports are part of the same power stack, and all power from the XPS and the switch is shared across all switches in the stack. Power sharing is the default mode, but the XPS supports the same stack power modes that are supported in a ring topology (strict and nonstrict power-sharing or redundant modes).

You can configure the XPS from any switch connected to an XPS port. If you enter XPS configuration commands on more than one switch, the last configuration applied takes effect. Only the switch and port name are saved in the switch configuration file.

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.

In a stack with only stack switches, all the Ethernet management ports on the stack members are connected to a hub to which the PC is connected. The active link is from the Ethernet management port on the through the hub, to the PC. If the activeswitch fails and a new active switch is elected, the active link is now from the Ethernet management port on the new active switch to the PC.

In a mixed stack, the stack members are connected to the PC through the Ethernet management ports. The active link is from the active switch to the PC. If the active switch fails and the elected active switch is not switch 2, the active link can be from a stack member to the PC.

By default, the Ethernet management port is enabled. The switch cannot route packets from the Ethernet management port to a network port, and the reverse. Even though the Ethernet management port does not support routing, you may need to enable routing protocols on the port.

In the above figure , if the Ethernet management port and the network ports are associated with the same routing process, the routes are propagated as follows:

• 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 between these ports cannot be sent or received. If this happens, data packet loops occur between the ports, which disrupt the switch and network operation. To prevent the loops, configure route filters to avoid routes between the Ethernet management port and the network ports.

The Ethernet management port supports these features:

• Express Setup (only in switch stacks)

• Network Assistant

• Telnet with passwords

• TFTP

• Secure Shell (SSH)

• DHCP-based autoconfiguration

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

• IP ping

• Interface features

  • Speed—10 Mb/s, 100 Mb/s, and autonegotiation

  • Duplex mode—Full, half, and autonegotiation

  • Loopback detection

• Cisco Discovery Protocol (CDP)

• DHCP relay agent

• IPv4 and IPv6 access control lists (ACLs)

• Routing protocols

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.

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.

This table shows the link states that result from auto-MDIX settings and correct and incorrect cabling.

A PoE-capable switch port automatically supplies power to one of these connected devices if the switch senses that there is no power on the circuit:

• a Cisco pre-standard powered device (such as a Cisco IP Phone or a Cisco Aironet Access Point)

• an IEEE 802.3af-compliant powered device

A powered device can receive redundant power when it is connected to a PoE switch port and to an AC power source. The device does not receive redundant power when it is only connected to the PoE port.

The following MTU values can be configured:

• System Jumbo MTU--This value applies to switched packets on the Gigabit Ethernet and 10-Gigabit Ethernet ports of the switch. Use the system mtu jumbo bytes global configuration command to specify the system jumbo MTU value.

• System Routing MTU--This value applies only to routed packets on all routed ports of the switch or switch stack. Use the system mtu routing global configuration command to specify the system routing MTU value.