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Cisco NX-OS and Virtual Device Contexts (VDCs)

Community Manager

The following content is taken from the Cisco Press book NX-OS and Cisco Nexus Switching: Next-Generation Data Center Architectures, by Kevin Corbin, Ron Fuller, and David Jansen.

Cisco built the next-generation data center-class operating system designed for maximum scalability and application availability. The NX-OS data center-class operating system was built with modularity, resiliency, and serviceability at its foundation. NX-OS is based on the industry-proven Cisco Storage Area Network Operating System (SAN-OS) Software and helps ensure continuous availability to set the standard for mission-critical data center environments. The self-healing and highly modular design of Cisco NX-OS enables for operational excellence increasing the service levels and enabling exceptional operational flexibility. Several advantages of Cisco NX-OS include the following:

  • Unified data center operating system
  • Robust and rich feature set with a variety of Cisco innovations
  • Flexibility and scalability
  • Modularity
  • Virtualization
  • Resiliency
  • IPv4 and IPv6 IP routing and multicast features
  • Comprehensive security, availability, serviceability, and management features

One key benefit of NX-OS is the use of VDCs. Cisco Nexus 7000 Series switches can be segmented into virtual devices based on customer requirements. VDCs offer several benefits such as fault isolation, administration plane, separation of data traffic, and enhanced security. This logical separation provides the following benefits:

  • Administrative and management separation
  • Change and failure domain isolation from other VDCs
  • Address, VLAN, VRF, and vPC isolation

Each VDC appears as a unique device and allows for separate Roles-Based Access Control Management (RBAC) per VDC. This enables VDCs to be administered by different administrators while still maintaining a rich, granular RBAC capability. With this functionality, each administrator can define virtual routing and forwarding instance (VRF) names and VLAN IDs independent of those used in other VDCs safely with the knowledge that VDCs maintain their own unique software processes, configuration, and data-plane forwarding tables.

Each VDC also maintains an individual high-availability (HA) policy that defines the action that the system will take when a failure occurs within a VDC. Depending on the hardware configuration of the system, there are various actions that can be performed. In a single supervisor system, the VDC can be shut down, restarted, or the supervisor can be reloaded. In a redundant supervisor configuration, the VDC can be shut down, restarted, or a supervisor switchover can be initiated.

There are components that are shared between VDC(s), which include the following:

  • A single instance of the kernel which supports all of the processes and VDCs
  • Supervisor modules
  • Fabric modules
  • Power supplies
  • Fan trays
  • System fan trays
  • CMP
  • CoPP
  • Hardware SPAN resources

This figure shows the logical segmentation with VDCs on the Nexus 7000. A common use case is horizontal consolidation to reduce the quantity of physical switches at the data center aggregation layer. In this figure, there are two physical Nexus 7000 chassis; the logical VDC layout is also shown.


VDC Configuration Examples

This section shows the required steps to creating a VDC; once the VDC is created, you will assign resources to the VDC. VDC(s) are always created from the default admin VDC context, VDC context 1.

Note: The maximum number of VDCs that can be configured per Nexus 7000 chassis is four; the default VDC (VDC 1) and three additional VDC(s).

This example shows how to configure the VDC core on Egypt:

egypt(config)# vdc core

Note:  Creating VDC, one moment please ...

egypt# show vdc

vdc_id  vdc_name             state         mac

------  --------             -----         ----------

1       egypt                active       00:1b:54:c2:38:c1

2       core                 active       00:1b:54:c2:38:c2

egypt# show vdc core detail

vdc id: 2
vdc name: core
vdc state: active
vdc mac address: 00:1b:54:c2:38:c2
vdc ha policy: RESTART
vdc dual-sup ha policy: SWITCHOVER
vdc boot Order: 2
vdc create time: Mon Feb 22 13:11:59 2010
vdc reload count: 1
vdc restart count: 0

Once the VDC is created, you now have to assign physical interfaces to the VDC. Depending on the Ethernet modules installed in the switch, interface allocation is supported as follows:

  • In the 32-port 10-Gigabit Ethernet Module (N7K-M132XP-12), interfaces can be allocated on a per port-group basis; there are eight port-groups. For example, port-group 1 are interfaces e1, e3, e5, e7; port-group 2 are interfaces e2, e4, e6, e8.
  • The 48-port 10/100/1000 I/O Module (N7K-M148GT-11) can be allocated on a per-port basis.
  • The 48-port 1000BaseX I/O Module (N7K-M148GS-11) can be allocated on a per-port basis.

In a future module, N7K-D132XP-15, the interfaces will be allocated per 2 ports per VDC.

Note: It is not possible to virtualize a physical interface and associate the resulting logical interfaces to different VDCs. A supported configuration is to virtualize a physical interface and associate the resulting logical interfaces with different VRFs or VLANs. By default, all physical ports belong to the default VDC.

This example demonstrates how to allocate interfaces to a VDC:

egypt(config)# vdc core

eqypt(config-vdc)# allocate interface Ethernet1/17

egypt(config-vdc)# allocate interface Ethernet1/18

To verify the interfaces allocation, enter the show vdc membership command as demonstrated in this example:

egypt(config-vdc)# show vdc membership

vdc_id: 1 vdc_name: egypt interfaces:

        Ethernet1/26          Ethernet1/28          Ethernet1/30

        Ethernet1/32          Ethernet2/2           Ethernet2/4

        Ethernet2/6           Ethernet2/8           Ethernet2/26

        Ethernet2/28          Ethernet2/30          Ethernet2/32

        Ethernet3/4           Ethernet3/5           Ethernet3/6

        Ethernet3/7           Ethernet3/8           Ethernet3/9

        Ethernet3/11          Ethernet3/12          Ethernet3/13

        Ethernet3/14          Ethernet3/15          Ethernet3/16

        Ethernet3/17          Ethernet3/18          Ethernet3/19

        Ethernet3/20          Ethernet3/21          Ethernet3/22

        Ethernet3/23          Ethernet3/24          Ethernet3/25

        Ethernet3/26          Ethernet3/27          Ethernet3/28

        Ethernet3/29          Ethernet3/30          Ethernet3/31

        Ethernet3/32          Ethernet3/33          Ethernet3/34

        Ethernet3/35          Ethernet3/36          Ethernet3/39

        Ethernet3/40          Ethernet3/41          Ethernet3/42

        Ethernet3/43          Ethernet3/44          Ethernet3/45

        Ethernet3/46          Ethernet3/47          Ethernet3/48

vdc_id: 2 vdc_name: core interfaces:

        Ethernet1/17          Ethernet1/18          Ethernet1/19

        Ethernet1/20          Ethernet1/21          Ethernet1/22

        Ethernet1/23          Ethernet1/24          Ethernet1/25

        Ethernet1/27          Ethernet1/29          Ethernet1/31

        Ethernet2/17          Ethernet2/18          Ethernet2/19

        Ethernet2/20          Ethernet2/21          Ethernet2/22

        Ethernet2/23          Ethernet2/24          Ethernet2/25

        Ethernet2/27          Ethernet2/29          Ethernet2/31

        Ethernet3/1           Ethernet3/2           Ethernet3/3


In addition to interfaces, other physical resources can be allocated to an individual VDC, including IPv4 route memory, IPv6 route memory, port-channels, and SPAN sessions. Configuring these values prevents a single VDC from monopolizing system resources. This example demonstrates how to accomplish this:

egypt(config)# vdc core

egypt(config-vdc)# limit-resource port-channel minimum 32 maximum equal-to-min

egypt(config-vdc)# limit-resource u4route-mem minimum 32 maximum equal-to-min

egypt(config-vdc)# limit-resource u6route-mem minimum 32 maximum equal-to-min

egypt(config-vdc)# limit-resource vlan minimum 32 maximum equal-to-min

egypt(config-vdc)# limit-resource vrf minimum 32 maximum equal-to-min

Defining the VDC HA policy is also done within the VDC configuration sub-mode. Use the ha-policy command to define the HA policy for a VDC as demonstrated in this example:

egypt(config)# vdc core

eqypt(config-vdc)# ha-policy dual-sup bringdown

The HA policy will depend based upon the use-case or VDC role. For example, if you have dual-supervisor modules in the Nexus 7000 chassis or if the VDC role is development/test, the VDC HA policy may be to just shut down the VDC. If the VDC role is for the core and aggregation use case, then the HA policy would be switchover.

NX-OS and Cisco Nexus Switching: Next-Generation Data Center Architectures

By Kevin Corbin, Ron Fuller, David Jansen.

ISBN-10: 1-58705-892-8

ISBN-13: 978-1-58705-892-9

Published: Jun 10, 2010

US SRP $54.00

Published by Cisco Press.
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