SAN Terminology – FCOE – Nexus 5k/2k

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So if you’re working Cisco at all these days, you’ve probably heard of the Nexus platform.  I’ve had some exposure to the 7k’s, but more recently we’ve been doing some testing with the 5k/2k platforms.  The 5k is a layer 2 switch, that allows FEX (Fabric Extender) modules to connect to them.  The FEX in this case, would be the Nexus 2k.  I like to think of the 2k as a line card in a 6500 chassis.  It has ASICs and is very much a layer 2 switch, but the brains of the operation are the 5k to which the 2ks connect.  To be clear, there is NO configuration done on the 2ks.  When the 2ks are connected to the 5ks, and the 5ks are configured for the FEXs, the ports from the FEX show up in the 5k configuration.  The idea is that the 5k could be a ‘middle of row’ data center solution with multiple 2ks hung off of it in adjoining racks.  This reduces the complexity of access layer switches since the only real configuration is on the 5k.

The other benefit of the 5k/2k solution is that they support 10 gig FCOE.  That is, with a fiber module in the 5k, I can connect the 5k to a SAN switch (MDS in most cases) and then extend a VSAN to the 5k.  The 5k can then associate the VSAN to a VLAN.  The access ports on the 2k are then configured as trunks, and allow traffic from both the SAN VLAN and the data VLAN (which is also connected to the 5k) to traverse a single link to the server.  The server then uses what are called  CNAs (Converged Network Adapter) to split the FC and IP traffic out and deliver it to the host.  So rather than having dual NICs (or more), and dual HBAs, we now have dual CNAs that deliver redundant paths to both the IP network as well as the SAN fabric.

It had been awhile since I worked with fiber channel, so to wrap up this post I’m going to define some of the basic terms/acronyms you should know about when working with this sort of technology.  Some will be obvious to many of you, but I’m going to cover all of the basics.  In following posts I plan on discussing NPV and NPIV, 5k/2k configuration, and troubleshooting steps for FCOE pertaining to the Nexus platform.

SAN/FC Terms and Acronyms
– Storage Area Network
FC – Fiber Channel
N(ode) Ports – End node port, either an HBA on a server, or a target on a storage array
F(abric) Ports – A port on a FC switch that is connected to the N port
E(xpansion) Port – A port on a FC switch that is connected to another FC switch
ISL – Inter Switch Link.  The connection between two E ports
WWN – World Wide Number.  A globally unique 64 bit number used to identify nodes on a SAN fabric
FLOGI – The fabric logon process
N Port address – Also called, N Port ID.  A 24 bit address that is automatically assigned to a WWN during the fabric login process.  The N port address is also commonly referred to as the Fiber Channel ID.

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