By default, Cisco Nexus devices switches operate in fabric mode. In this mode, the switch provides standard Fibre Channel switching capability and features.
In fabric mode, each switch that joins a SAN is assigned a domain ID. Each SAN (or VSAN) supports a maximum of 239 domain IDs, so the SAN has a limit of 239 switches. In a SAN topology with a large number of edge switches, the SAN may need to grow beyond this limit. NPV alleviates the domain ID limit by sharing the domain ID of the core switch among multiple edge switches.
In NPV mode, the edge switch relays all traffic from server-side ports to the core switch. The core switch provides F port functionality (such as login and port security) and all the Fibre Channel switching capabilities.
The edge switch appears as a Fibre Channel host to the core switch and as a regular Fibre Channel switch to its connected devices.
The following figure shows an interface-level view of an NPV configuration.
Figure 1. NPV Interface Configuration
In NPV mode, the edge switch relays all traffic to the core switch, which provides the Fibre Channel switching capabilities. The edge switch shares the domain ID of the core switch.
To convert a switch into NPV mode, you set the NPV feature to enabled. This configuration command automatically triggers a switch reboot. You cannot configure NPV mode on a per-interface basis. NPV mode applies to the entire switch.
In NPV mode, a subset of fabric mode CLI commands and functionality is supported. For example, commands related to fabric login and name server registration are not required on the edge switch, because these functions are provided in the core switch. To display the fabric login and name server registration databases, you must enter the show flogi database and show fcns database commands on the core switch.
Server interfaces are F ports on the edge switch that connect to the servers. A server interface may support multiple end devices by enabling the N port identifier virtualization (NPIV) feature. NPIV provides a means to assign multiple FC IDs to a single N port, which allows the server to assign unique FC IDs to different applications.
To use NPIV, enable the NPIV feature and reinitialize the server interfaces that will support multiple devices.
In Cisco Nexus devices, server interfaces can be virtual Fibre Channel interfaces.
All interfaces from the edge switch to the core switch are configured as proxy N ports (NP ports).
An NP uplink is a connection from an NP port on the edge switch to an F port on the core switch. When an NP uplink is established, the edge switch sends a fabric login message (FLOGI) to the core switch, and then (if the FLOGI is successful) it registers itself with the name server on the core switch. Subsequent FLOGIs from end devices connected to this NP uplink are forwarded as-is to the core switch.
In the switch CLI configuration commands and output displays, NP uplinks are called External Interfaces.
In Cisco Nexus devices, NP uplink interfaces are virtual Fibre Channel interfaces.
When deploying NPV traffic management, follow these guidelines:
Use NPV traffic management only when automatic traffic engineering does not meet your network requirements.
You do not need to configure traffic maps for all server interfaces. By default, NPV will use automatic traffic management.
NPV Guidelines and Limitations
When configuring NPV, note the following guidelines and limitations:
In-order data delivery is not required in NPV mode because the exchange between two end devices always takes the same uplink from the edge switch to the core. Upstream of the edge switch, core switches will enforce in-order delivery if configured.
You can configure zoning for end devices that are connected to edge switches using all available member types on the core switch. For fWWN, sWWN, domain, or port-based zoning, use the fWWN, sWWN, domain, or port of the core switch in the configuration commands.
Port tracking is not supported in NPV mode.
Port security is supported on the core switch for devices logged in through the NPV switch. Port security is enabled on the core switch on a per-interface basis. To enable port security on the core switch for devices that log in through an NPV switch, you must adhere to the following requirements:
The internal FLOGI must be in the port security database; in this way, the port on the core switch will allow communications and links.
All the end device pWWNs must also be in the port security database.
Servers can be connected to the switch when in NPV mode.
Targets can not be connected to the switch when in NPV mode.
Fibre Channel switching is not performed in the edge switch; all traffic is switched in the core switch.
NPV supports NPIV-capable module servers. This capability is called nested NPIV.
Only VF and VNP port types are supported in NPV mode.
When you enable NPV, the system configuration is erased and the switch reboots.
We recommend that you save your current configuration either in boot flash memory or to a TFTP server before you enable NPV.
To enable NPV, perform this task:
Command or Action
switch# configure terminal
Enters configuration mode.
switch(config)# npv enable
Enables NPV mode. The switch reboots, and it comes back up in NPV mode.
A write-erase is performed during the initialization.
switch(config-npv)# nonpv enable
Disables NPV mode, which results in a reload of the switch.
Configuring NPV Interfaces
After you enable NPV, you should configure the NP uplink interfaces and the server interfaces.
Configures a mapping between a server interface (or range of server interfaces) and an NP uplink interface (or range of NP uplink interfaces).
switch(config)# no npv traffic-map server-interfacevfcvfc-idexternal-interface vfcvfc-id
Removes the mapping between the specified server interfaces and NP uplink interfaces.
Enabling Disruptive Load Balancing
If you configure additional NP uplinks, you can enable the disruptive load-balancing feature to distribute the server traffic load evenly among all the NP uplinks.
To enable disruptive load balancing, perform this task:
Command or Action
switch# configure terminal
Enters configuration mode on the NPV.
switch(config)# npv auto-load-balance disruptive
Enables disruptive load balancing on the switch.
switch (config)# no npv auto-load-balance disruptive
Disables disruptive load balancing on the switch.
To display information about NPV, perform the following task:
Command or Action
switch# show npv flogi-table [all]
Displays the NPV configuration.
Verifying NPV Examples
To display a list of devices on a server interface and their assigned NP uplinks, enter the show npv flogi-table command on the Cisco Nexus device:
switch# show npv flogi-table
INTERFACE VSAN FCID PORT NAME NODE NAME INTERFACE
vfc31 1 0xee0008 10:00:00:00:c9:60:e4:9a 20:00:00:00:c9:60:e4:9a vfc21
vfc31 1 0xee0009 20:00:00:00:0a:00:00:01 20:00:00:00:c9:60:e4:9a vfc22
vfc31 1 0xee000a 20:00:00:00:0a:00:00:02 20:00:00:00:c9:60:e4:9a vfc23
vfc31 1 0xee000b 33:33:33:33:33:33:33:33 20:00:00:00:c9:60:e4:9a vfc24
Total number of flogi = 4
For each server interface, the External Interface value displays the assigned NP uplink.
To display the status of the server interfaces and the NP uplink interfaces, enter the show npv status command:
switch# show npv status
npiv is enabled
Interface: vfc21, VSAN: 1, FCID: 0x1c0000, State: Up
Interface: vfc22, VSAN: 1, FCID: 0x040000, State: Up
Interface: vfc23, VSAN: 1, FCID: 0x260000, State: Up
Interface: vfc24, VSAN: 1, FCID: 0x1a0000, State: Up
Number of External Interfaces: 4
Interface: vfc31, VSAN: 1, NPIV: No, State: Up
Number of Server Interfaces: 1
To view fcns database entries for NPV edge switches, you must enter the show fcns database command on the core switch.
To view all the NPV edge switches, enter the show fcns database command on the core switch:
core-switch# show fcns database
For additional details (such as IP addresses, switch names, interface names) about the NPV edge switches that you see in the show fcns database output, enter the show fcns database detail command on the core switch:
core-switch# show fcns database detail
Verifying NPV Traffic Management
To display the NPV traffic map, enter the show npv traffic-map command.