Stumped - 3850 Intermittent Issue

[dustin.k.mcaninch]

Hello,

I am troubleshooting a 3850 switch inside a US Military vehicle. All connections go through a patch panel before going to the switch.

I am having trouble staying connected to the switch when going through the patch panel. It goes up for a half a second and then down for 3-5 seconds and then back up for a half second and repeats.

It works fine when I bypass the patch panel and plug directly into the switch.

This problem exists with the two different workstations with identical NICs. 

It works fine through the patch panel when I use other NICs.

I'll break it down so it's not so confusing:

I have two identical NICs (same model / different MACs) that work fine directly to switch but not through patch panel.

All other NICs (different models than above) work fine through patch panel and directly to switch.

I'm stumped. 

I would appreciate any help I can get.

The switch logs just show it going up and down when plugged into patch panel. 

I guess my question is this:

Why would a specific type of model of NIC have trouble connecting through a patch panel but work fine when plugged directly into the switch?

Update: I have discovered that when I manually change the link speed on the NIC from "Auto-negotiate" to 10Mbps Full Duplex, it works perfectly through the patch panel. It does not work when I manually select faster speeds.....

This speed is obviously way too slow so is there a solution?

Thanks!

.

[Georg Pauwen]

Hello,

tough one. I guess what you could check are the IPv4 Properties of your NICs (Advanced tab) and check if there are any differences in the settings. What NICs do not work ?

And are you logging in through TELNET, SSH ?

[dustin.k.mcaninch]

I am using a serial console cable to reach the switch, not ssh or telnet. I am using ping and link lights to determine connectivity to the switch with the workstations though. 

All settings seem to be the same. I also noted that manually lower the link speed on the NIC to 10 Mbps fixes the issue but it shouldn't be the solution. 😞

Thanks for replying!

[Georg Pauwen]

Hello,

10Mbs works...what cable are you actually using, can you determine the category (5/6/6e) ? Have you tried and user a different cable ? Sorry for asking dumb questions...

What manufacturers are the non-working NICs from ?

[Elliot Dierksen]

Is it possible that the cable plant behind the patch panel is not twisted properly? I have seen case with higher speed ethernet (100Mb+) didn't work over untwisted pairs. Your description of the problem points strongly towards a cable plant problem.

[Leo Laohoo]

If going through a patch panel the link flaps? 

What firmware version is the switch on? 

Has anyone done a TDR on the link to determine if there is a line fault?  

How to use Time-Domain Reflectometer (TDR)

[dustin.k.mcaninch · Accepted solution]

UPDATE:

I have resolved the issue. The ports that lead to the outside of the vehicle have a hub protector attached to them. This hub protector serves as lightning or surge protector for the switch since these ports lead outside. I replaced this hub protector with another one and everything is working fine now.

Here is a link to the hub protector if anyone is curious: http://www.bravobravo.us/pdfs/lan_protectors/4port/RJ45LAN8HUB.pdf

Thanks for the help!!