Information About Layer 3 Interfaces
Layer 3 interfaces forward IPv4 and IPv6 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.
You cannot configure a shared interface as a Layer 3 interface. See the Cisco NX-OS FCoE Configuration Guide for Cisco Nexus 7000 and Cisco MDS 9500 for information on shared interfaces.
Beginning with Cisco Release 5.2(1), you can configure a Fabric Extender (FEX) port as a Layer 3 interface for host connectivity, but not for routing. See the Configuring the Cisco Nexus 2000 Series Fabric Extender for more information on fabric extenders.
This section includes the following topics:
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 routed 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.
Beginning with Cisco Release 4.2(1), you can assign a static MAC address to a Layer 3 interface. By default, the MAC address for the Layer 3 interfaces is the MAC address of the VDC it is assigned to. For information on configuring MAC addresses, see the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x.
You can also create a Layer 3 port channel from routed interfaces. For more information on port channels, see Chapter6, “Configuring Port Channels”
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 virtual local area network (VLAN) 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.
Figure 4-1 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 carried by the trunking port.
Figure 4-1 Subinterfaces for VLANs
For more information on VLANs, see the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x.
VLAN Interfaces
A VLAN interface or switch virtual interfaces (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 see configure it. Beginning in Cisco NX-OS Release 4.2, the system automatically takes a checkpoint prior to disabling the feature, and you can rollback to this checkpoint. See Cisco Nexus 7000 Series NX-OS System Management Configuration Guide, Release 5.x, for information on rollbacks and checkpoints.
You must configure the VLAN network interface in the same VDC as the VLAN.
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 Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x.
Figure 4-2 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 4-2 Connecting Two VLANs with VLAN interfaces
Note You can configure VLAN interface for inband management in the Cisco Nexus 7000 Series switches with the F1 Series modules in the chassis.
Loopback Interfaces
A loopback interface is a virtual interface with a single endpoint that is always up. Any packet transmitted over a loopback interface is immediately received by this interface. Loopback interfaces emulate a physical interface. You can configure up to 1024 loopback interfaces per VDC, numbered 0 to 1023.
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.
Tunnel Interfaces
Cisco NX-OS supports tunnel interfaces as IP tunnels. IP tunnels can encapsulate a same-layer or higher layer protocol and transport the result over IP through a tunnel created between two routers. See “Configuring IP Tunnels,” for more information on IP tunnels.
High Availability
Layer 3 interfaces support stateful and stateless restarts. After the switchover, Cisco NX-OS applies the runtime configuration after the switchover.
See the Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide, Release 5.x, for complete information on high availability.
Virtualization Support
Layer 3 interfaces support Virtual Routing and Forwarding instances (VRFs). VRFs exist within virtual device contexts (VDCs). By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF. A Layer 3 logical interface (VLAN interface, loopback) configured in one VDC is isolated from a Layer 3 logical interface with the same number configured in another VDC. For example, loopback 0 in VDC 1 is independent of loopback 0 in VDC 2.
You can configure up to 1024 loopback interfaces per VDC.
You can associate the interface with a VRF. For VLAN interfaces, you must configure the VLAN interface in the same VDC as the VLAN.
See the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 5.x, for information about VDCs and see the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for information about configuring an interface in a VRF.
Note You must assign an interface to a VRF before you configure the IP address for that interface.
Configuring Layer 3 Interfaces
This section includes the following topics:
Configuring a Routed Interface
You can configure any Ethernet port as a routed interface.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1. configure terminal
2. interface ethernet slot/port
3. no switchport
4. ip address ip-address/length
or
ipv6 address ipv6-address/length
5. (Optional) show interfaces
6. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
interface ethernet slot/port Example: switch(config)# interface ethernet 2/1 switch(config-if)# |
Enters interface configuration mode. |
Step 3 |
no switchport Example: switch(config-if)# no switchport |
Configures the interface as a Layer 3 interface and deletes any configuration specific to Layer 2 on this interface. |
Step 4 |
ip address ip-address/length Example: switch(config-if)# ip address 192.0.2.1/8 |
Configures an IP address for this interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IP addresses. |
ipv6 address ipv6-address/length Example: switch(config-if)# ipv6 address 2001:0DB8::1/8 |
Configures an IPv6 address for this interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IPv6 addresses. |
Step 5 |
show interfaces Example : switch(config-if)# show interfaces ethernet 2/1 |
(Optional) Displays the Layer 3 interface statistics. |
Step 6 |
copy running-config startup-config Example: switch(config)# copy running-config startup-config |
(Optional) Saves this configuration change. |
Use the medium command to set the interface medium to either point to point or broadcast.
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medium { broadcast | p2p } Example: switch(config-if)# medium p2p |
Configures the interface medium as either point to point or broadcast. |
Note The default setting is broadcast, and this setting does not appear in any of the show commands. However, if you do change the setting to p2p, you will see this setting when you enter the show running config command.
Use the switchport command to convert a Layer 3 interface into a Layer 2 interface.
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switchport Example: switch(config-if)# switchport |
Configures the interface as a Layer 2 interface and deletes any configuration specific to Layer 3 on this interface. |
This example shows how to configure a routed interface:
switch# configure terminal
switch(config)# i nterface 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
The default setting for interfaces is routed. If you want to configure an interface for Layer 2, enter the switchport command. Then, if you change a Layer 2 interface to a routed interface, enter the no switchport command.
Configuring a Subinterface
You can configure one or more subinterfaces on a routed interface or on a port channel made from routed interfaces.
BEFORE YOU BEGIN
Configure the parent interface as a routed interface.
See the “Configuring a Routed Interface” section.
Create the port-channel interface if you want to create a subinterface on that port channel.
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1. configure terminal
2. interface ethernet slot/port.number
3. ip address ip-address/length
or
ipv6 address ipv6-address/length
4. encapsulation dot1q vlan-id
5. (Optional) show interfaces
6. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
interface ethernet slot/port.number Example: switch(config)# interface ethernet 2/1.1 switch(config-subif)# |
Creates a subinterface and enters subinterface configuration mode. The number range is from 1 to 4094. |
Step 3 |
ip address ip-address/length Example: switch(config-subif)# ip address 192.0.2.1/8 |
Configures an IP address for this subinterface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IP addresses. |
ipv6 address ipv6-address/length Example: switch(config-subif)# ipv6 address 2001:0DB8::1/8 |
Configures an IPv6 address for this subinterface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IPv6 addresses. |
Step 4 |
encapsulation dot1Q vlan-id Example: switch(config-subif)# encapsulation dot1Q 33 |
Configures IEEE 802.1Q VLAN encapsulation on the subinterface. The range is from 2 to 4093. |
Step 5 |
show interfaces Example : switch(config-subif)# show interfaces ethernet 2/1.1 |
(Optional) Displays the Layer 3 interface statistics. |
Step 6 |
copy running-config startup-config Example: switch(config-subif)# copy running-config startup-config |
(Optional) Saves this configuration change. |
This example shows how to create a subinterface:
switch# configure terminal
switch(config)# i nterface ethernet 2/1.1
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. Higher layer protocols use bandwidth parameter to calculate path costs. You can configure the bandwidth on a subinterface with one of the following methods:
- Explicit—Set the bandwidth value for the subinterface directly.
- Inherit—Set the bandwidth that all subinterfaces inherit from the parent interface as either a specific value or as the bandwidth of the parent interface.
If you do not set the subinterface bandwidth or configure it to inherit the bandwidth from the parent interface, Cisco NX-OS determines the subinterface bandwidth as follows:
- If the parent interface is up, then the bandwidth of the subinterface is the same as the operational speed of the parent interface. For ports, the subinterface bandwidth is the configured or negotiated link speed. For port channels, the subinterface bandwidth is the aggregate of the link speeds of individual members of the port channel.
- If the parent interface is down, then the bandwidth of the subinterface depends on the type of parent interface:
– Port-channel subinterfaces have 100-Mb/s bandwidth for subinterfaces.
– 1-Gb/s Ethernet ports have 1-Gb/s bandwidth for subinterfaces.
– 10-Gb/s Ethernet ports have 10-Gb/s bandwidth for subinterfaces.
To configure the bandwidth of an interface, use the following command in interface mode:
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bandwidth Example: switch(config-if)# bandwidth 100000 |
Configures the bandwidth parameter for a routed interface, port channel, or subinterface. |
To configure subinterfaces to inherit the bandwidth from the parent interface, use the following command in interface mode:
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bandwidth inherit [ value ] Example: switch(config-if)# bandwidth inherit 100000 |
Configures all subinterfaces of this interface to inherit the bandwidth value configured. If you do not configure the value, the subinterfaces inherit the bandwidth of the parent interface. The range is from 1 to 10000000, in kilobytes. |
Configuring a VLAN interface
You can create VLAN interfaces to provide inter-VLAN routing.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1. configure terminal
2. feature interface-vlan
3. interface vlan number
4. ip address ip-address/length
or
ipv6 address ipv6-address/length
5. (Optional) show interface vlan number
6. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
Example: switch(config)# feature interface-vlan |
Enables VLAN interface mode. |
Step 3 |
interface vlan number Example: switch(config)# interface vlan 10 switch(config-if)# |
Creates a VLAN interface. The number range is from 1 to 4094. |
Step 4 |
ip address ip-address/length Example: switch(config-if)# ip address 192.0.2.1/8 |
Configures an IP address for this VLAN interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IP addresses. |
ipv6 address ipv6-address/length Example: switch(config-if)# ipv6 address 2001:0DB8::1/8 |
Configures an IPv6 address for this VLAN interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IPv6 addresses. |
Step 5 |
show interface vlan number Example : switch(config-if)# show interface vlan 10 |
(Optional) Displays the Layer 3 interface statistics. |
Step 6 |
copy running-config startup-config Example: switch(config-if)# copy running-config startup-config |
(Optional) Saves this configuration change. |
This example shows how to create a VLAN interface:
switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# in terface vlan 10
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# copy running-config startup-config
Configuring Inband Management in the Nexus Chassis
You can a create VLAN interface for inband management in the Cisco Nexus 7000 Series switches when there are only F1 Series modules in the chassis.
Caution
We recommend that you use a dedicated VLAN for inband management on the F1 Series modules. Do not run data traffic on the VLAN that you are using for inband management.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1. configure terminal
2. feature interface-vlan
3. interface vlan number
4. no shutdown
5. management
6. ip address ip-address/length
7. (Optional) show interface vlan number
8. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
switch(config)# feature interface-vlan
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Creates a loopback interface. The range is from 0 to 1023. |
Step 3 |
interface vlan number Example: switch(config)# interface vlan 10 switch(config-if)# |
Creates a VLAN interface. The number range is from 1 to 4094. Note Configure the VLAN and add the interfaces. |
Step 4 |
Example: switch(config-if)# no shutdown |
Brings an interface administratively up (enable/disable an interface). |
Step 5 |
Example: switch(config-if)# management |
Allows in-band management access to a VLAN interface IP address. |
Step 6 |
ip address ip-address/length Example: switch(config-if)# ip address 192.0.2.1/8 |
Configures an IP address for this VLAN interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IP addresses. |
Step 7 |
show interface vlan number Example : switch(config-if)# show interface vlan 10 |
(Optional) Displays the Layer 3 interface statistics. |
Step 8 |
copy running-config startup-config Example: switch(config-if)# copy running-config startup-config |
(Optional) Saves this configuration change. |
This example shows how to create an inband management in the Cisco Nexus 7000 chassis:
switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# in terface vlan 5
switch(config)# no shutdown
switch(config)# management
switch(config-if)# ip address 192.0.2.1/8
switch(config-if)# copy running-config startup-config
Configuring a Loopback Interface
You can configure a loopback interface to create a virtual interface that is always up.
BEFORE YOU BEGIN
Ensure that the IP address of the loopback interface is unique across all routers on the network.
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1. configure terminal
2. interface loopback instance
3. ipv4 address ip-address
or
ipv6 address ip-address
4. (Optional) show interfaces loopback instance
5. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
interface loopback instance Example: switch(config)# interface loopback 0 switch(config-if)# |
Creates a loopback interface. The range is from 0 to 1023. |
Step 3 |
ip address ip-address/length Example: switch(config-if)# ip address 192.0.2.100/8 |
Configures an IP address for this interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for more information on IP addresses. |
ipv6 address ipv6-address/length Example: switch(config-if)# ipv6 address 2001:0DB8::18/8 |
Configures an IPv6 address for this interface. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x , for more information on IPv6 addresses. |
Step 4 |
show interfaces loopback instance Example : switch(config-if)# show interfaces loopback 0 |
(Optional) Displays the loopback interface statistics. |
Step 5 |
copy running-config startup-config Example: switch(config-if)# copy running-config startup-config |
(Optional) Saves this configuration change. |
This example shows how to create a loopback interface:
switch# configure terminal
switch(config)# in terface 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
You can add a Layer 3 interface to a VRF.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Assign the IP address for a tunnel interface after you have configured the interface for a VRF.
SUMMARY STEPS
1. configure terminal
2. interface interface-type number
3. vrf member vrf-name
4. ip-address ip-prefix/length
5. (Optional) show vrf [ vrf-name ] interface interface-type number
6. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters configuration mode. |
Step 2 |
interface interface-type number Example : switch(config)# interface loopback 0 switch(config-if)# |
Enters interface configuration mode. |
Step 3 |
vrf member vrf-name Example: switch(config-if)# vrf member RemoteOfficeVRF |
Adds this interface to a VRF. |
Step 4 |
ip address ip-prefix/length Example: switch(config-if)# ip address 192.0.2.1/16 |
Configures an IP address for this interface. You must do this step after you assign this interface to a VRF. |
Step 5 |
show vrf [ vrf-name ] interface interface-type number Example : switch(config-vrf)# show vrf Enterprise interface loopback 0 |
(Optional) Displays VRF information. |
Step 6 |
copy running-config startup-config Example: switch(config)# copy running-config startup-config |
(Optional) Saves this configuration change. |
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