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Category: FCoE

FCoE between data centers? Forget it!

Was anyone trying to sell you the “wonderful” idea of running FCoE between Data Centers instead of FC-over-DWDM or FCIP? Sounds great ... until you figure out it won’t work. Ever ... or at least until switch vendors drastically increase interface buffers on the 10GE ports.

FCoE requires lossless Ethernet between its “routers” (Fiber Channel Forwarders – see Multihop FCoE 101 for more details), which can only be provided with Data Center Bridging (DCB) standards, specifically Priority Flow Control (PFC). However, if you want to have lossless Ethernet between two points, every layer-2 (or higher) device in the path has to support DCB, which probably rules out any existing layer-2+ solution (including Carrier Ethernet, pseudowires, VPLS or OTV). The only option is thus bridging over dark fiber or a DWDM wavelength.

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FCoE, QCN and Frame Relay analogies

Just when I hoped we were finally getting somewhere with the FCoE/QCN discussion, Brocade managed to muddy the waters with its we-still-don’t-know-what-it-is announcement. Not surprisingly, networking consultants like my friend Greg Ferro of the Etherealmind fame responded to the shenanigan with statements like “FCoE ... is a technology so mindboggingly complicated that marketing people can argue over competing claims and all be correct.” Not true, the whole thing is exceedingly simple once you understand the architecture (and the marketing people always had competing claims).

Pretend for a minute that FC ≈ IP and LAN bridging ≈ Frame Relay, teleport into this parallel universe and allow me to tell you the whole story once again in more familiar terms.

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Does FCoE need QCN (802.1Qau)?

One of the recurring religious FCoE-related debates of the last months is undoubtedly “do you need QCN to run FCoE” with Cisco adamantly claiming you don’t (hint: Nexus doesn’t support it) and HP claiming you do (hint: their switch software lacks FC stack) ... and then there’s this recent announcement from Brocade (more about it in a future post). As is usually the case, Cisco and HP are both right ... depending on how you design your multi-hop FCoE network.

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What exactly is a Nexus 4000?

Someone mentioned a while ago in a comment to one of my blog posts that the Nexus 4000 switch already supports multihop FCoE. Now that we know what multihop FCoE really is, let’s see how Nexus 4000 fits into the picture.

The Cisco Nexus 4000 Series Design Guide starts with a confusing set of claims:

  • The Cisco Nexus 4000 Series Switches provide the Fibre Channel Forwarder (FCF) function.
  • Nexus 4000 is a FCoE Initialization Protocol (FIP) snooping bridge.
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Storage networking is like SNA

I’m writing this post while travelling to the Net Field Day 2010, the successor to the awesome Tech Field Day 2010 during which the FCoTR technology was launched. It’s thus only fair to extend that fantastic merger of two technologies we all love, look at the bigger picture and compare storage networking with SNA.


  • If you’re too young to understand what I’m talking about, don’t worry. Yes, you’ve missed all the beauties of RSRB/DLSw, CIP, APPN/APPI and the likes, but major technology shifts happen every other decade or so, so you’ll be able to use FC/FCoE/iSCSI analogies the next time (and look like a dinosaur to the rookies). Make sure, though, that you read the summary.
  • I’ll use present tense throughout the post when comparing both environments although SNA should be mostly history by now.
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FCoE and DCB standards

The debate whether the DCB standards are complete or not and thus whether FCoE is a standard-based technology are entering the metaphysical space (just a few more blog posts and they will join the eternal angels-on-a-hairpin problem), but somehow the vendors are not yet talking about the real issues: when will we see the standards implemented in shipping products and will there be a need to upgrade the hardware.

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