Monday Sep 25

Posts Tagged ‘layer 1’

Mar
19/08
Layer 1: Mr Bump and the Bad Wire
Last Updated on Tuesday, 12 August 2008 03:52
Written by JJ
Wednesday, March 19th, 2008
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No, not a bad Mr Bump, or a bad Bump in the Wire… But one of the Bumpster’s recent posts brings about a good topic for mention- bad cable (or wire, as is more appropriate for his post).

In his friendly KISS-it note, he shares a story to remind us of our Layer 1 woes. I can’t TELL you how many times there’s a mystery problem… which almost always later surfaces as a physical dis-connect or mis-connect along the way.

In fact, just last night a certain someone called me from the road while setting up a demo… after hours of agony (and fixing some other issues) the final problem was- YEP- a cable in the wrong spot.

It’s something that happens to all of us- certainly nothing to be ashamed of. And it doesn’t always work out to be a misplaced cable… quite frequently we see bad cables, older cheap Cat 5 that’s not behaving well, home-made ends that corrode or break and even the occasional patching mis-match (see my previous post on 568A vs B).

Don’t we feel stupid after hours (or days) of puzzling, only to find out there’s a piece of metal, plastic or fiber to blame?

Here are a few Tips & Tricks to check Layer 1 and possibly eliminate frustration when you have your next ‘mystery’ problem:

  • Cable placement. Obvious one, but check and double-check, then have someone else check. It’s like proof-reading your own writing.
  • Cable REplacement. If you’re not sure- just replace the cable when possible with a known good. (Note the ‘known good’, I’ve seen batches of lemons more than once).
  • Ditch Home Mades. This little gem comes from my father- many years ago, he started noticing home-made cable ends (even those made with the BEST crimping tools) would eventually deteriorate. It may be fatigue, corrosion or little aliens- you can’t always be 100% sure of the cause, but it happens more often than not.
  • Don’t Bend It. If you are working with fiber, be nice to the fiber… wrap it gently in loose coils. Don’t bend it, squish it or let it get crimped in the cable management. You may know this, but others rummaging in your closet may not.
  • Check Negotiation. Hop in the switch or device interface and see what speed and duplex it auto-negotiated to. This culprit is probably a close 2nd behind finding bad cables.
  • Check Neighbors. A good way to dig around and investigate a possible Layer 1 issue is to jump back in that switch interface and do a show arp or show neighbors (clear old first) and see if you what you think should be there is actually there.( Pings can work too, but it’s possible ICMP is disabled, so I prefer the former method personally.)
  • Check Patching Termination. Instead of repeating myself, I’ll direct you to the recent post on 568A vs B. You’ll usually see this when you upgrade from 10/100 to Gig.

Layer 1 is the FIRST thing we check for when doing a site survey or network migration plan. If you don’t get that one right, the others are surely to fail… which may take you to Layers 8 & 9… and as we know- we like to stay a 7 and below. ;)

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