Autonegotiated speed for LAN always 100 Mbps

Question

I am at the earliest stages of setting up XG Firewall Home. Internet to the house is via gigabit fiber. 
 After going through the initial configuration, Port1 (the LAN port) always configures itself as 100 Mbps - full duplex - autonegotiated. I am using a multiport NIC (Intel 350). The WAN port (Port2) configures itself correctly to 1000 Mbps - full duplex - autonegotiated. As both Ports/NICs are identical, I cannot determine why the LAN/Internal network is limiting itself, out of the box, to 100 Mbps. 
 I have tried manually changing the settings for Port1, as shown here ( https://community.sophos.com/kb/en-us/123517 ) to 1000 Mbps - full duplex, but that causes Port1 to go offline. I can manually restore to auto via commandline, and, again, it goes back to 100 Mbps. The only I have tried connecting to Port1 with different computers with gigabit ethernet adaptors, and nothing changes. 
 I would appreciate any advice you could give me, as I would like to take advantage of the gigabit fiber internet speed, which seems to be correctly received by Port2 (the WAN port). Thanks in advance.

rfcat_vk · Accepted Answer

Hi, 
 how would like to edit your post so it is more easily read. 
 If you have a 1gb/s switch put it between the failing port and your test device. I would suspect a faulty cable. 
 Ian

Brian Weinberg · Answer

Hi Ian, 
 I'm sorry you find it difficult to read. I was trying to layout everything clearly and concisely. Perhaps, I overdid it. ;-) 
 Thank you for your quick response. 
 The cable that I was using was brand new, out of the bag, so I didn't consider it as a possibility, but, you are correct, that was it. Sometimes, the easiest answer is the best answer. 
 I appreciate your help! 
 Brian