Something odd

Started by Nerm, August 27, 2015, 01:37:46 PM

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Nerm

August 27, 2015, 01:37:46 PM
Had an issue today where a Sonicwall and a cable modem would not auto-negotiate or work hard coded full-duplex. Hard coded half-duplex they worked fine. After a little troubleshooting discovered that this issue only happened when the client's cables they had onsite were used. If I used one of my cables it worked fine. Their cables were Cat5e and terminated 568-b just like mine. Here is where it gets weirder. Their cables worked fine with my laptop connected to either the cable modem or Sonicwall but not when they were connected together. Of course the resolution was one of my new cables but anyone seen something like this or have a possible explanation?

deanwebb

#1
August 27, 2015, 01:42:16 PM
What kind of cables do you have? Also, are the client cables less than 3 feet long?
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NetworkGroover

#2
August 27, 2015, 01:49:08 PM
Quote from: Nerm on August 27, 2015, 01:37:46 PM
Had an issue today where a Sonicwall and a cable modem would not auto-negotiate or work hard coded full-duplex. Hard coded half-duplex they worked fine. After a little troubleshooting discovered that this issue only happened when the client's cables they had onsite were used. If I used one of my cables it worked fine. Their cables were Cat5e and terminated 568-b just like mine. Here is where it gets weirder. Their cables worked fine with my laptop connected to either the cable modem or Sonicwall but not when they were connected together. Of course the resolution was one of my new cables but anyone seen something like this or have a possible explanation?

Mmmm no, but things like these I usually pick my battles and choose not to burn a lot of time on it unless I literally have nothing to do. 

When you say terminated 568-b - what do you mean?  On both ends?  Sounds like a networking 101 kind of issue but the tx/rx half-duplex stuff eludes me at the moment... anyway I'm probably horribly wrong so I'll just shush. :P
Engineer by day, DJ by night, family first always

routerdork

#3
August 27, 2015, 02:17:35 PM
I had a modem from TimeWarner cable several years ago that connected to my Cisco ASA. For some reason even though the cable modem was auto/auto I still had to hard code the ASA for full duplex. It's the only time I've ever come across that specific scenario. After upgrading service and getting a different modem the issue went away. My modem with the issue looked something like the one in the link. http://mydeviceinfo.comcast.net/device.php?devid=310 Can't say that I ever thought of trying a different cable.
"The thing about quotes on the internet is that you cannot confirm their validity." -Abraham Lincoln

Nerm

#4
August 27, 2015, 02:24:07 PM
The cables onsite were just generic bulk indoor cabling cut to length of about 2' and terminated. The cable that worked was a pre-terminated 1' patch cable.

When I say 568b I mean just standard straight-through ethernet termination.

Oddly this was a TWC cable modem. Not the same one routerdork linked to though. I have had issues with Cisco products and TWC cable modems in the past but those issues were never the cable itself.
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