Cisco Nexus 6000 Series NX-OS Interfaces Configuration Guide, Release 6.0(2)N1(1)
Configuring Layer 3 Interfaces
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Configuring Layer 3 Interfaces

This chapter contains the following sections:

Information About Layer 3 Interfaces

Layer 3 interfaces forward packets to another device using static or dynamic routing protocols. You can use Layer 3 interfaces for IP routing and inter-VLAN routing of Layer 2 traffic.

Routed Interfaces

You can configure a port as a Layer 2 interface or a Layer 3 interface. A routed interface is a physical port that can route IP traffic to another device. A routed interface is a Layer 3 interface only and does not support Layer 2 protocols, such as the Spanning Tree Protocol (STP).

All Ethernet ports are switched interfaces by default. You can change this default behavior with the CLI setup script or through the system default switchport command.

You can assign an IP address to the port, enable routing, and assign routing protocol characteristics to this routed interface.

You can assign a static MAC address to a Layer 3 interface. For information on configuring MAC addresses, see the Layer 2 Switching Configuration Guide for your device.

You can also create a Layer 3 port channel from routed interfaces.

Routed interfaces and subinterfaces support exponentially decayed rate counters. Cisco NX-OS tracks the following statistics with these averaging counters:
  • Input packets/sec
  • Output packets/sec
  • Input bytes/sec
  • Output bytes/sec

Subinterfaces

You can create virtual subinterfaces on a parent interface configured as a Layer 3 interface. A parent interface can be a physical port or a port channel.

Subinterfaces divide the parent interface into two or more virtual interfaces on which you can assign unique Layer 3 parameters such as IP addresses and dynamic routing protocols. The IP address for each subinterface should be in a different subnet from any other subinterface on the parent interface.

You create a subinterface with a name that consists of the parent interface name (for example, Ethernet 2/1) followed by a period and then by a number that is unique for that subinterface. For example, you could create a subinterface for Ethernet interface 2/1 named Ethernet 2/1.1 where .1 indicates the subinterface.

Cisco NX-OS enables subinterfaces when the parent interface is enabled. You can shut down a subinterface independent of shutting down the parent interface. If you shut down the parent interface, Cisco NX-OS shuts down all associated subinterfaces as well.

One use of subinterfaces is to provide unique Layer 3 interfaces to each VLAN that is supported by the parent interface. In this scenario, the parent interface connects to a Layer 2 trunking port on another device. You configure a subinterface and associate the subinterface to a VLAN ID using 802.1Q trunking.

The following figure shows a trunking port from a switch that connects to router B on interface E 2/1. This interface contains three subinterfaces that are associated with each of the three VLANs that are carried by the trunking port.

Figure 1. Subinterfaces for VLANs



VLAN Interfaces

A VLAN interface or a switch virtual interface (SVI) is a virtual routed interface that connects a VLAN on the device to the Layer 3 router engine on the same device. Only one VLAN interface can be associated with a VLAN, but you need to configure a VLAN interface for a VLAN only when you want to route between VLANs or to provide IP host connectivity to the device through a virtual routing and forwarding (VRF) instance that is not the management VRF. When you enable VLAN interface creation, Cisco NX-OS creates a VLAN interface for the default VLAN (VLAN 1) to permit remote switch administration.

You must enable the VLAN network interface feature before you can configure it. The system automatically takes a checkpoint prior to disabling the feature, and you can roll back to this checkpoint. For information about rollbacks and checkpoints, see the System Management Configuration Guide for your device.


Note

You cannot delete the VLAN interface for VLAN 1.

You can route across VLAN interfaces to provide Layer 3 inter-VLAN routing by configuring a VLAN interface for each VLAN that you want to route traffic to and assigning an IP address on the VLAN interface. For more information on IP addresses and IP routing, see the Unicast Routing Configuration Guide for your device.

The following figure shows two hosts connected to two VLANs on a device. You can configure VLAN interfaces for each VLAN that allows Host 1 to communicate with Host 2 using IP routing between the VLANs. VLAN 1 communicates at Layer 3 over VLAN interface 1and VLAN 10 communicates at Layer 3 over VLAN interface 10.

Figure 2. Connecting Two VLANs with VLAN Interfaces



Loopback Interfaces

A loopback interface is a virtual interface with a single endpoint that is always up. Any packet that is transmitted over a loopback interface is immediately received by this interface. Loopback interfaces emulate a physical interface.

You can use loopback interfaces for performance analysis, testing, and local communications. Loopback interfaces can act as a termination address for routing protocol sessions. This loopback configuration allows routing protocol sessions to stay up even if some of the outbound interfaces are down.

Licensing Requirements for Layer 3 Interfaces

Although the Cisco Nexus 6000 Series switch has Layer 3 interfaces inherent in the device, you must still install the Layer 3 Base Services Package feature licence to use basic Layer 3 features and functionality. For advanced Layer 3 features, you must install the Layer 3 Advanced Enterprise Package feature license. For a complete explanation fo the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

After installing a Layer 3 license, the following guidelines and limitations apply to the device:

  • In Service Software Upgrades (ISSUs) are not supported.
  • Temporary Layer 3 feature licenses are not supported. (The Layer 3 Base Services Package license has a grace period of 0.)
  • Management Switch Virtual Interfaces (SVIs) are supported without a Layer 3 Base Services Package license, and ISSU can be performed with Management SVIs configured.
  • All SVIs (whether management keyword is configured or not) are operationally up when no Layer 3 Base Services Package license is installed. After the Layer 3 Base Services Packages feature license is installed, routed SVIs are brought operationally down and then brought back up again. This reload happens because the routed SVIs behave like management SVIs before a Layer 3 Base Services Packages feature license is installed, and the interface state saved in the hardware needs to be cleared followed by programming of the SVI routes in the Forwarding Information Base (FIB).
  • If you have not enabled any Layer 3 features or configured any Layer 3 interfaces, you can clear a Layer 3 license without having to reload the device. Then, you can perform a non-disruptive ISSU.
  • After clearing a Layer 3 license, you must copy the running-configuration to the startup-configuration and reload the device. Then, you can perform a non-disruptive ISSU.
  • After clearing a Layer 3 license, you must copy the running-configuration to the startup-configuration and reload the device. Then, you can perform a non-disruptive ISSU.
  • Although HSRP and VRRP do not need to be removed before clearing a Layer 3 license, we recommend that you clear their configurations as well.
  • Although VRRP and HSRP can be configured without a Layer 3 license, they will not work without a Layer 3 license. If they are configured, non-disruptive ISSU is not supported.

Guidelines and Limitations for Layer 3 Interfaces

Layer 3 interfaces have the following configuration guidelines and limitations:
  • If you change a Layer 3 interface to a Layer 2 interface, Cisco NX-OS shuts down the interface, reenables the interface, and removes all configuration specific to Layer 3.
  • If you change a Layer 2 interface to a Layer 3 interface, Cisco NX-OS shuts down the interface, reenables the interface, and deletes all configuration specific to Layer 2.

Default Settings for Layer 3 Interfaces

The default setting for the Layer 3 Admin state is Shut.

Configuring Layer 3 Interfaces

Configuring a Routed Interface

Procedure
     Command or ActionPurpose
    Step 1switch# configure terminal 

    Enters global configuration mode.

     
    Step 2switch(config)# interface ethernet slot/port 

    Enters interface configuration mode.

    Note   

    If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

     
    Step 3switch(conifg-if)# no switchport 

    Configures the interface as a Layer 3 interface and deletes any configuration specific to Layer 2 on this interface.

    Note   

    To convert a Layer 3 interface back into a Layer 2 interface, use the switchport command.

     
    Step 4switch(config-if)# [ip | ipv6 ]ip-address/length 

    Configures an IP address for this interface.

     
    Step 5switch(config-if)# show interfaces  (Optional)

    Displays the Layer 3 interface statistics.

     
    Step 6switch(config-if)# copy running-config startup-config  (Optional)

    Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

     

    This example shows how to configure an IPv4 routed Layer 3 interface:

    switch# configure terminal
switch(config)# interface ethernet 2/1
switch(config-if)# no switchport
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# copy running-config startup-config

    Configuring a Subinterface

    Before You Begin
    • Configure the parent interface as a routed interface.
    • Create the port-channel interface if you want to create a subinterface on that port channel.
    Procedure
       Command or ActionPurpose
      Step 1switch(config-if)# copy running-config startup-config  (Optional)

      Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

       
      Step 2switch(config)# interface ethernet slot/port.number
       

      Enters interface configuration mode. The range for the slot is from 1 to 255. The range for the port is from 1 to 128.

      Note   

      If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

       
      Step 3switch(config-if)# [ip | ipv6] address ip-address/length 

      Configures IP address for this interface.

       
      Step 4switch(config-if)# encapsulation dot1Q vlan-id  Configures IEEE 802.1Q VLAN encapsulation on the subinterface. The range for the vlan-id is from 2 to 4093. 
      Step 5switch(config-if)# show interfaces  (Optional)

      Displays the Layer 3 interface statistics.

       
      Step 6switch(config-if)# copy running-config startup-config  (Optional)

      Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

       

      This example shows how to create a subinterface:

      switch# configure terminal
switch(config)# interface ethernet 2/1
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# encapsulation dot1Q 33
switch(config-if)# copy running-config startup-config

      Configuring the Bandwidth on an Interface

      You can configure the bandwidth for a routed interface, port channel, or subinterface.

      Procedure
         Command or ActionPurpose
        Step 1switch# configure terminal 

        Enters global configuration mode.

         
        Step 2switch(config)# interface ethernet slot/port 

        Enters interface configuration mode. The range for the slot is from 1 to 255. The range for the port is from 1 to 128.

        Note   

        If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

         
        Step 3switch(conifg-if)# bandwidth [value | inherit [value]]  Configures the bandwidth parameter for a routed interface, port channel, or subinterface, as follows:
        • value—Size of the bandwidth in kilobytes. The range is from 1 to 10000000.
        • inherit—Indicates that all subinterfaces of this interface inherit either the bandwidth value (if a value is specified) or the bandwidth of the parent interface (if a value is not specified).
         
        Step 4switch(config-if)# copy running-config startup-config  (Optional)

        Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

         

        This example shows how to configure Ethernet interface 2/1 with a bandwidth value of 80000:

        switch# configure terminal
switch(config)# interface ethernet 2/1
switch(config-if)# bandwidth 80000
switch(config-if)# copy running-config startup-config

        Configuring a VLAN Interface

        Procedure
           Command or ActionPurpose
          Step 1switch# configure terminal 

          Enters global configuration mode.

           
          Step 2switch(config)# feature interface-vlan 

          Enables VLAN interface mode.

           
          Step 3switch(config)# interface vlan number 

          Creates a VLAN interface. The number range is from 1 to 4094.

           
          Step 4switch(config-if)# [ip | ipv6 ] address ip-address/length 

          Configures an IP address for this interface.

           
          Step 5switch(config-if)# no shutdown 

          Brings the interface up administratively.

           
          Step 6switch(config-if)# show interface vlan number  (Optional)

          Displays the VLAN interface statistics. The number range is from 1 to 4094.

           
          Step 7switch(config-if)# copy running-config startup-config  (Optional)

          Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

           

          This example shows how to create a VLAN interface:

          switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# interface vlan 10
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# copy running-config startup-config

          Configuring a Loopback Interface

          Before You Begin

          Ensure that the IP address of the loopback interface is unique across all routers on the network.

            Procedure
               Command or ActionPurpose
              Step 1switch# configure terminal 

              Enters global configuration mode.

               
              Step 2switch(config)# interface loopback instance 

              Creates a loopback interface. The instance range is from 0 to 1023.

               
              Step 3switch(config-if)# [ip | ipv6 ] address ip-address/length 

              Configures an IP address for this interface.

               
              Step 4switch(config-if)# show interface loopback instance  (Optional)

              Displays the loopback interface statistics. The instance range is from 0 to 1023.

               
              Step 5switch(config-if)# copy running-config startup-config  (Optional)

              Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

               

              This example shows how to create a loopback interface:

              switch# configure terminal
switch(config)# interface loopback 0
switch(config-if)# ip address 192.0.2.100/8
switch(config-if)# copy running-config startup-config

              Assigning an Interface to a VRF

              Before You Begin

              Assign the IP address for a tunnel interface after you have configured the interface for a VRF.

                Procedure
                   Command or ActionPurpose
                  Step 1switch# configure terminal 

                  Enters global configuration mode.

                   
                  Step 2switch(config)# interface interface-typenumber 

                  Enters interface configuration mode.

                   
                  Step 3switch(conifg-if)#vrf member vrf-name 

                  Adds this interface to a VRF.

                   
                  Step 4switch(config-if)# [ip | ipv6]ip-address/length 

                  Configures an IP address for this interface. You must do this step after you assign this interface to a VRF.

                   
                  Step 5switch(config-if)# show vrf [vrf-name] interface interface-type number  (Optional)

                  Displays VRF information.

                   
                  Step 6switch(config-if)# show interfaces  (Optional)

                  Displays the Layer 3 interface statistics.

                   
                  Step 7switch(config-if)# copy running-config startup-config  (Optional)

                  Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                   

                  This example shows how to add a Layer 3 interface to the VRF:

                  switch# configure terminal 
switch(config)# interface loopback 0 
switch(config-if)# vrf member RemoteOfficeVRF 
switch(config-if)# ip address 209.0.2.1/16 
switch(config-if)# copy running-config startup-config

                  Verifying the Layer 3 Interfaces Configuration

                  Use one of the following commands to verify the configuration:

                  Command

                  Purpose

                  show interface ethernet slot/port

                  Displays the Layer 3 interface configuration, status, and counters (including the 5-minute exponentially decayed moving average of inbound and outbound packet and byte rates).

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port brief

                  Displays the Layer 3 interface operational status.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port capabilities

                  Displays the Layer 3 interface capabilities, including port type, speed, and duplex.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port description

                  Displays the Layer 3 interface description.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port status

                  Displays the Layer 3 interface administrative status, port mode, speed, and duplex.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port.number

                  Displays the subinterface configuration, status, and counters (including the f-minute exponentially decayed moving average of inbound and outbound packet and byte rates).

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface port-channel channel-id.number

                  Displays the port-channel subinterface configuration, status, and counters (including the 5-minute exponentially decayed moving average of inbound and outbound packet and byte rates).

                  show interface loopback number

                  Displays the loopback interface configuration, status, and counters.

                  show interface loopback number brief

                  Displays the loopback interface operational status.

                  show interface loopback number description

                  Displays the loopback interface description.

                  show interface loopback number status

                  Displays the loopback interface administrative status and protocol status.

                  show interface vlan number

                  Displays the VLAN interface configuration, status, and counters.

                  show interface vlan number brief

                  Displays the VLAN interface operational status.

                  show interface vlan number description

                  Displays the VLAN interface description.

                  show interface vlan number private-vlan mapping

                  Displays the VLAN interface private VLAN information.

                  show interface vlan number status

                  Displays the VLAN interface administrative status and protocol status.

                  Monitoring Layer 3 Interfaces

                  Use one of the following commands to display statistics about the feature:

                  Command

                  Purpose

                  show interface ethernet slot/port counters

                  Displays the Layer 3 interface statistics (unicast, multicast, and broadcast).

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port counters brief

                  Displays the Layer 3 interface input and output counters.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port counters detailed [all]

                  Displays the Layer 3 interface statistics. You can optionally include all 32-bit and 64-bit packet and byte counters (including errors).

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port counters error

                  Displays the Layer 3 interface input and output errors.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port counters snmp

                  Displays the Layer 3 interface counters reported by SNMP MIBs. You cannot clear these counters.

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface ethernet slot/port.number counters

                  Displays the subinterface statistics (unicast, multicast, and broadcast).

                  Note   

                  If this is a 10G breakout port, the slot/port syntax is slot/QSFP-module/port.

                  show interface port-channel channel-id.number counters

                  Displays the port-channel subinterface statistics (unicast, multicast, and broadcast).

                  show interface loopback number counters

                  Displays the loopback interface input and output counters (unicast, multicast, and broadcast).

                  show interface loopback number counters detailed [all]

                  Displays the loopback interface statistics. You can optionally include all 32-bit and 64-bit packet and byte counters (including errors).

                  show interface loopback number counters errors

                  Displays the loopback interface input and output errors.

                  show interface vlan number counters

                  Displays the VLAN interface input and output counters (unicast, multicast, and broadcast).

                  show interface vlan number counters detailed [all]

                  Displays the VLAN interface statistics. You can optionally include all Layer 3 packet and byte counters (unicast and multicast).

                  show interface vlan counters snmp

                  Displays the VLAN interface counters reported by SNMP MIBs. You cannot clear these counters.

                  Configuration Examples for Layer 3 Interfaces

                  This example shows how to configure Ethernet subinterfaces:
                  switch# configuration terminal
switch(config)# interface ethernet 2/1.10
switch(config-if)# description Layer 3 for VLAN 10
switch(config-if)# encapsulation dot1q 10
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# copy running-config startup-config
                  This example shows how to configure a VLAN interface:
                  switch# configuration terminal
switch(config)# interface vlan 100


switch(config-if)# ipv6 address 33:0DB::2/8
switch(config-if)# copy running-config startup-config
                  This example shows how to configure a loopback interface:
                  switch# configuration terminal
switch(config)# interface loopback 3

switch(config-if)# ip address 192.0.2.2/32
switch(config-if)# copy running-config startup-config

                  Related Documents for Layer 3 Interfaces

                  Related Topics Document Title

                  Command syntax

                  For details about command syntax, see the command reference for your device.

                  IP

                  “Configuring IP” chapter in the Unicast Routing Configuration Guide for your device.

                  VLAN

                  “Configuring VLANs” chapter in the Layer 2 Switching Configuration Guide for your device.

                  MIBs for Layer 3 Interfaces

                  MIB MIB Link

                  IF-MIB

                  To locate and download MIBs, go to the following URL:

                  http:/​/​www.cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

                  CISCO-IF-EXTENSION-MIB

                  ETHERLIKE-MIB

                  Standards for Layer 3 Interfaces

                  No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.