Virtual Device Context (vdc) Overview and Configuration example

Below is the very basic explanation of cisco vdc and i hope you will be able to understand by reading it once only

Cisco's virtual device context or vdc is basically a concept of dividing a single Nexus 7000 hardware box into multiple logical boxes in such a way that they look like different physical device to a remote user/operator and each of the provisioned logical devices is configured and managed as if it were a separate physical device.
For example, you have a data center where you have deployed Nexus 7k in datacenter. Now, there are few other companies who don't have enough money to expend in setting up Nexus 7000 so they come to you to host a data center for them. You can simply virtualize your nexus 7000 into multiple virtual switches and can assign one logical portion(that is called vdc)  to one company. When they will login to their logical switch (looks like a separate physical switch to user) they can do whatever they want, other logical partition i.e. other vdc will remain unaffected. You can create vlans with same name/number in all vdc's and they will not interfere with each other. A particular vdc operator will not even come to know that same switch is being used by multiple user virtually. Only Admin can create/delete vdc's and from Admin vdc only, we can see other vdcs.

Similary, vdc can be used to create different test and production traffic. In my previous project, we created one vdc for test environment in order to test new implementation/protocol etc and another vdc for production traffic. If our test used to successful in our test environment, then only we used to put them into production.

How many vdc we can create?? hmm...it depends which supervisor engine you are using.
-If you are using SUP1, then you can create upto 4 vdc's. All of them can be used to carry data traffic and you can create/delete vdcs from default vdc which can also be used for data traffic.
-if you are using SUP2, then you can create 1 admin + 4 data vdc. That means, you can not use admin vdc for data traffic. That will be used for only admin purpose i.e. managing other vdc's.
-if you are using SUP2E, then you can create 1+8 vdc, where 1 admin plus 8 production vdc.

Within VDC it can contain its own unique and independent set of VLANs and VRFs. Each VDC can have assigned to it physical ports, thus allowing for the hardware data plane to be virtualized as well. Within each VDC, a separate management domain can manage the VDC itself, thus allowing the management plane itself to also be virtualized.

physical interfaces cannot be shared by multiple VDCs. This one-to-one assignment of physical interfaces to VDCs is at the basis of complete isolation among the configured contexts. However, there are two exceptions:
• The out-of-band management interface (mgmt0) can be used to manage all VDCs. Each VDC has its own representation for mgmt0 with a unique IP address that can be used to send syslog, SNMP and other management information.
• When a storage VDC is configured, a physical interface can belong to one VDC for Ethernet traffic and to the storage VDC for FCoE traffic. Traffic entering the shared port is sent to the appropriate VDC according to the frame's EtherType. Specifically, the storage VDC will get the traffic with EtherType 0x8914 for FCoE Initialization Protocol (FIP) and 0x8906 for FCoE.
Physical interfaces can be assigned to a VDC with a high degree of freedom. However, there are differences among different I/O modules because of the way the VDC feature is enforced at the hardware level. The easy way to learn the specific capabilities of the installed hardware is by entering the show interface x/y capabilities command to see the port group associated with a particular interface.

Switch Resources that Can Be Allocated to a VDC:

Physical Interfaces, PortChannels, Bridge Domains and VLANs, HSRP and GLBP Group IDs, and SPAN

Switch Resources that Cannot Be Allocated to a VDC:

CPU*, Memory*, TCAM Resources such as the FIB, QoS, and Security ACLs

  * Future releases may allow allocation of CPU or memory to a VDC.

VDC configuration is so easy. 

step 1   Log in to the default VDC with a username that has the network-admin role.

Step 2   Enter configuration mode and create the VDC using the default settings.

N7k# configure terminal

N7k(config)# vdc WDECAIB

Note:  Creating VDC, one moment please ...

switch(config-vdc)#

                

Step 3   (Optional) Allocate interfaces to the VDC.

N7k(config-vdc)# allocate interface ethernet 1/1-8

similarly more interfaces can be assigned. below is the screenshot of a vdc configuration.

Initially, all physical interfaces belong to the default VDC (VDC 1). When you create a new VDC, the Cisco NX-OS software creates the virtualized services for the VDC without allocating any physical interfaces to it. After you create a new VDC, you can allocate a set of physical interfaces from the default VDC to the new VDC.

The interface allocation is the most important part of vdc configuration. You can not assign ports of same port-group to different vdc.If you are unable to assign any interface to particular vdc or some ports are being automatically being assigned, then it could be port-grouping issue. Port group is basicaly how many parts are on same hardware ASIC. So, if 4 ports are on same ASIC, then they all must be in same vdc as they are sharing and being operated by same asic.  How many port-groups are there in my card or is there a fix formula? Basically it depends which type of I/O module card we are using. for example:

•N7K-M202CF-22L (1 interface x 2 port groups = 2 interfaces 100G modules)—There are no restrictions on the interface allocation between VDCs.

•N7K-M206FQ-23L (1 interface x 6 port groups = 6 interfaces 40G modules)—There are no restrictions on the interface allocation between VDCs.

•N7K-M224XP-23L (1 interface x 24 port groups = 24 interfaces 10G modules)—There are no restrictions on the interface allocation between VDCs.

•N7K-M108X2-12L (1 interface x 8 port groups = 8 interfaces)—There are no restrictions on the interface allocation between VDCs.

•N7K-M148GS-11L, N7K-M148GT-11, and N7K-M148GS-11 (12 interfaces x 4 port groups = 48 interfaces)—There are no restrictions on the interface allocation between VDCs, but we recommend that interfaces that belong to the same port group be in a single VDC.

•N7K-M132XP-12 (4 interfaces x 8 port groups = 32 interfaces)—Interfaces belonging to the same port group must belong to the same VDC. See the example for this module in Figure 1-3.

•N7K-M148GT-11L (same as non-L M148) (1 interface x 48 port groups = 48 interfaces)—There are no restrictions on the interface allocation between VDCs.

•N7K-M132XP-12L (same as non-L M132) (1 interface x 8 port groups = 8 interfaces)—All M132 cards require allocation in groups of 4 ports and you can configure 8 port groups.


================
Switching between VDC's

If you have logged into default VDC, you can use “Show VDC” command to see what all other vdc’s have been created.

IF you want to switch to any other vdc from default vdc, you can use “switchto vdc <vdc name>” command as shown below and if you have logged into user created vdc WDECAIB  from default vdc using switchto command, you can use “switchback” command to come back to default vdc, however, if you have directly ssh/telnet into user created vdc WDECAIB  here, you can not do a “switchback” to come into default vdc.

I hope it was helpful. You can read through my blog to know more about vdc's like vdc users etc.