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Network Dictionary – Mythinformation

15th July 2008 By 6 Comments

Mythinformation is the term used to describe some form of knowledge that is based on apocryphal, false or old knowledge. A play on the the word misinformation.

A classic piece of mythinformation is the belief the Ethernet auto-sensing does not work. The stories of a misconfigured Ethernet ports causing major problems are either mythical or based in the past when there were no accepted standards for auto-negotiation.

The only instance for locking duplex/speed is when using obselete equipment, or when you do not know the configuration of the remote side. In fact, forcing speed and duplex reduces Ethernet functionality. For Gigabit Ethernet particularly, disabling auto-negotiation will almost definitely cause poor performance and outages when the Gigabit Ethernet line gets heavily congested.

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About Greg Ferro

Greg Ferro is a Network Engineer/Architect, mostly focussed on Data Centre, Security Infrastructure, and recently Virtualization. He has over 20 years in IT, in wide range of employers working as a freelance consultant including Finance, Service Providers and Online Companies. He is CCIE#6920 and has a few ideas about the world, but not enough to really count.

He is a host on the Packet Pushers Podcast, blogger at EtherealMind.com and on Twitter @etherealmind and Google Plus

  • http://pl.atyp.us Jeff Darcy

    I think you could have picked a better example. Autoneg *does* fail on a lot of equipment which is arguably either obsolete or cheap or both, but still quite common even in serious data centers. I’ve seen it with my own eyes, it’s no myth, and don’t go all No True Scotsman on me by saying anything that fails autoneg is obsolete by definition. If you want a real myth, how about the one about the “vast majority” of servers not being able to generate 1GE worth of HBA traffic? That’s apocryphal, false, or old for you.

    • http://etherealmind.com Greg Ferro

      I have a different experience. The only autoneg problems I have seen in the last 3 years where when someone else wasn’t using it, or when the cabling was faulty. Hard setting bypassed the faulty cabling, by in the long term it did cause errors and was replaced.

      And yes, I and others, still believe that. However, it gonna be pretty subjective, your experience may be with high quality servers with good HBA / TOE / setup parameters and that will make the difference, but most people don’t have that setup or that experience so I still stand by my statement.

      I also know that it will not true in the future, but, hey, its a moving target.

  • http://pl.atyp.us Jeff Darcy

    There’s a pattern here: you haven’t *personally* seen something so you dismiss it as a myth. Well, I’ve seen the things you claim are mythical. I have several dozen I/O nodes in my lab at work, each of which is a real-life counterexample to your “1GE worth of HBA traffic” claim. The kicker is that, on an individual basis, each of those nodes is not very expensive or powerful. This laptop could beat one on most tasks. Clearly it’s the *non*existence of such things that’s a myth. The target has *already* moved.

    Yes, you have a different experience. You can stand by your statements all you like, but that doesn’t make them true. My experiences aren’t mythical; I prefer to think of them as legendary. ;)

    • http://etherealmind.com Greg Ferro

      “My experiences arenít mythical; I prefer to think of them as legendary”

      Great line, just brilliant.

  • Pingback: Autonegotiation on Ethernet – it works, it should be mandatory! | My Etherealmind

  • Ivan Brunello

    Just two notes:
    1) Never dealt with OOOOOLD cabling, which still uses 2-pairs patches on PC110 connectors. Well, we had to manually force our gigabit switch to run 100 FD.

    2) On the other hand, talking about Cisco equipment, I found old FastEthernet switches were really a mess w/ autosensing; it worked no more than 50% of cases.
    BUT, autonegotiation on gigabit-class ones (not only against gigabit hosts, but also down to FastEthernet) was indeed really working.