Business Network Mystery

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dukesinatra

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Jan 31, 2018
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Laptop A successfully connects to any number of wall-data-ports in our office with a DHCP assigned IP. Connectivity is confirmed via sending emails and accessing non-cached websites. Each wall-data-port is connected to a patch panel and corresponding Cisco switch thirty feet away.

Laptop A does not connect successfully to one particular wall-data-port (Wall-Data-Port A). The task-bar icon on Laptop A shows Connected with Internet Access, but the device pulls a 169.x.x.x IP and cannot reach any networked resources.

Strangely, Laptops B, C and D are able to successfully connect to the Wall-Data-Port A with full internet access.

I have rebooted, released and renewed the IP on Laptop A. I have also swapped the Ethernet cable and I tried other ports on the the switch (all with the same results when Laptop A is connected). Finally, I confirmed that the switchport is assigned to the correct VLAN. As a final measure of troubleshooting, I deleted all network drivers on Laptop A and reinstalled. No joy.

It would appear that Laptop A is the common denominator in this scenario. What is going on here?

 
Solution
D
ISSUE RESOLVED FINALLY
Update *05 March 2018*
The issue was resolved by replacing the network cable between the patch panel and the switch. A couple of pins in the terminated connection were shorted causing data to drop and allowing for an inconsistent connection.
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2Be_or_Not2Be

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Aug 23, 2013
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I agree - definitely a logical issue as the hardware seems to have been ruled out. What you mentioned is very likely, and they can also check ACLs/filters.
 
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Solandri

Solandri

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Jan 4, 2012
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Actually I've seen similar issues with mis-wired Ethernet cable runs. If you don't follow the T-568A/B wiring, the signal pairs don't match up with the twisted pairs, and the wires can pick up more noise. Some Ethernet adapters deal with this noise better than others, resulting in a cable or wall port where some devices work, others don't. The shortest run I've seen this happen was about 30 feet, which is only 10% of Ethernet's max length spec. So the strength of a nearby noise source would seem to matter more than the length of the mis-wired run. Have someone in IT confirm that the wall port and its opposite end in the switch room is wired correctly.

The odd thing to me is why the laptop shows a network and Internet connection, when it has a 169.x.x.x IP address. I thought the connectivity icon was dependent on a valid IP configuration. Can it show full connection even if you're not getting a valid IP configuration via DHCP?
 
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D

dukesinatra

Prominent
Jan 31, 2018
2
0
520
ISSUE RESOLVED FINALLY
Update *05 March 2018*
The issue was resolved by replacing the network cable between the patch panel and the switch. A couple of pins in the terminated connection were shorted causing data to drop and allowing for an inconsistent connection.
 
Upvote 0 Downvote
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