NPV and NPIV
May 8, 2012 67 Comments
The CCIE Data Center blueprint makes mention of NPV and NPIV, and Cisco UCS also makes heavy use of both topics, topics that many may be unfamiliar with most. This post (part of my CCIE Data Center prep series) will explain what they do, and how they’re different.
(Another great post on NPV/NPIV is from Scott Lowe, and can be found here. This is a slightly different approach to the same information.)
NPIV and NPV are among the two most ill-named of acronyms I’ve come across in IT, especially since they sound very similar, yet do two fairly different things. NPIV is an industry-wide term and is short for N_Port ID Virtualization, and NPV is a Cisco-specific term, and is short for N_Port Virtualization. Huh? Yeah, not only do they sound similar, but the names give very little indication as to what they do.
First, let’s talk about NPIV. To understand NPIV, we need to look at what happens in a traditional Fibre Channel environment.
When a host plugs into a Fibre Channel switch, the host end is called an N_Port (Node Port), and the FC switch’s interface is called an F_Port (Fabric Port). The host has what’s known as a WWPN (World Wide Port Name, or pWWN), which is a 64-bit globally unique label very similar to a MAC address.
However, when a Fibre Channel host sends a Fibre Channel frame, that WWPN is no where in the header. Instead, the host does a Fabric Login, and obtains an FCID (somewhat analagous to an IP addres). The FCID is a 24-bit number, and when FC frames are sent in Fibre Channel, the FCID is what goes into the source and destination fields of the header.
Note that the first byte (08) of the FCID is the same domain ID as the FC switch that serviced the host’s FLOGI.
In regular Fibre Channel operations, only one FCID is given per physical port. That’s it. It’s a 1 to 1 relationship.
But what if you have an ESXi host, for example, with virtual fibre channel interfaces. For those virtual fibre channel interfaces to complete a fabric login (FLOGI), they’ll need their own FCIDs. Or, what if you don’t want to have a Fibre Channel switch (such as an edge or blade FC switch) go full Fibre Channel switch?
NPIV lets a FC switch give out multiple FCIDs on a single port. Simple as that.
The magic of NPIV: One F_Port gives out multiple FCIDs on (0x070100 to the ESXi host and 0x070200 and 0x070300 to the virtual machines)
NPV: Engage Cloak!
NPV is typically used on edge devices, such as a ToR Fibre Channel switch or a FC switch installed in a blade chassis/infrastruture. What does it do? I’m gonna lay some Star Trek on you.
NPV is a clocking device for a Fibre Chanel switch.
Wait, did you just compare Fibre Channel to a Sci-Fi technology?
How is NPV like a cloaking device? Essentially, an NPV enabled FC switch is hidden from the Fibre Channel fabric.
When a Fibre Channel switch joins a fabric, it’s assigned a Domain_ID, and participates in a number of fabric services. With this comes a bit of baggage, however. See, Fibre Channel isn’t just like Ethernet. A more accurate analogue to Fibre Channel would be Ethernet plus TCP/IP, plus DHCP, distributed 802.1X, etc. Lots of stuff is going on.
And partly because of that, switches from various vendors tend not to get a long, at least without enabling some sort of Interopability Mode. Without interopability mode, you can’t plug a Cisco MDS FC switch into say, a Brocade FC switch. And if you do use interopability mode and two different vendors in the same fabric, there are usually limitations imposed on both switches. Because of that, not many people build multi-vendor fabrics.
Easy enough. But what if you have a Cisco UCS deployment, or some other blade system, and your Fibre Channel switches from Brocade? As much as your Cisco rep would love to sell you a brand new MDS-based fabric, there’s a much easier way.
Engage the cloaking device.
(Note: NPV is a Cisco-specific term, while other vendors have NPV functionality but call it something else, like Brocade’s Access Gateway.) A switch in NPV mode is invisible to the Fibre Channel fabric. It doesn’t participate in fabric services, doesn’t get a domain ID, doesn’t do fabric logins or assign FCIDs. For all intents and purposes, it’s invisible to the fabric, i.e. cloaked. This simplifies deployments, saves on domain IDs, and lets you plug switches from one vendor into a switch of another vendor. Plug a Cisco UCS Fabric Interconnect into a Brocade FC switch? No problem. NPV. Got a Qlogic blade FC switch plugging into a Cisco MDS? No problem, run NPV on the Qlogic blade FC switch (and NPIV on the MDS).
The hosts perform fabric logins just like they normally would, but the NPV/cloaked switch passes FLOGIs up to the NPIV enabled port on the upstream switch. The FCID of the devices bears the the Domain ID of the upstream switch (and appears directly attached to the upstream switch).
The NPV enabled switch just proxies the FLOGIs up to the upstream switch. No fuss, no muss. Different vendors can interoperate, we save domain IDs, and it’s typically easier to administer.
TL;DR: NPIV allows multiple FLOGIs (and multiple FCIDs issued) from a single port. NPV hides the FC switch from the fabric.