Embarrassing Ethernet Issue Solved

Forum|Forum|4 years ago
October 6, 2021
5 replies
6091 views

I am a network engineer so keep the laughter down to a minimum. I had a situation where I was replacing my Cisco ASA5505 with a Fortigate 40F. I had all kinds of issues with throughput and SSL resets from my Cisco phone after the swap.

The Cisco ASA5505 only has 100Mbps Ethernet interfaces. 100Mbps is a 4 wire Ethernet configuration using 1,2,3,6 pins of the 4 wires. The Fortigate has 1000Mbp eight wire interfaces.

For some reason, when the AT&T technician installed my modem and ran the Ethernet cable back to where my firewall was set up, he split the 8 wires into 2 four wire jacks. I did not know this.

What I found out. I could not get the Fortigate to negotiate 1000Mbps with the modem. I used the 100Mbps setting thinking I had something wrong with the modem. I replaced the modem and it still did not work.

One day I was looking at the two jacks laying on the floor, one with a connection to the Fortigate and one sitting empty. I thought to myself what is that? I blew away all the dust to see what the AT&T technician did and thought oh no, this is the issue.

I re-terminated the ends to be a single cable and all was fixed.

Toshi_Esumi

SuperUser

I would re-wire and make all 8 wires go into one jack. It's an old method when T1+CAT3 cable was very common. We used to do that for inside wiring even for Ethernet to save cables. But no more because of PoE. It's no longer a practical/effective practice other than creating confusion and mistakes when they're repurposed, just like in your case.

wkana

New Member

No laughter here. I too am a Network Engineer and have had my fair share of "oh no" what is this scenarios. Sometimes the solution is sitting right there, just not yet readily viewable.

aagrafi

New Member

This reminds me of the 90s, where the cabling installers used to split the UTP cable and terminated the wire pairs in two plugs. One was used for data and the other was for telephone. This way they saved money, by using less cable. Back then, the Ethernet was running at 10 Mbps (10BaseT) and the telephone signal did not add too much noise. Now, with speeds of 1/10Gbps this would be impossible. I thought that such cabling practices had been disappeared nowadays, but it seems they haven't.

sw2090

SuperUser

with business telephony this is still done. As one UP0 POrt only uses two wires one can split pne rj45 up so you can have 4xup0 over one cable...

rwpatterson

New Member

I do that all the time with my copper lines, BUT I make an octopus RJ-45 plug -> 4 x RJ-11 jacks. No reconstruction necessary and doesn't void any cabling warranties. Of course this only works if the far end has all the copper in one area.

Sign up

Login with SSO

Login to the community

Login with SSO