Link partner advertised link modes - 100Mbps/half duplex quandry

[_zero]

My backup NAS, with a 1Gbps network capbility, has a direct Ethernet connection to a RT-AX86U LAN jack. But it connects ar 100Mbps (half-duplex).

When I run ethtool, it tells me:
Link partner advertised link modes:
100baseT/Half

From that I infer its "link partner" to be the router.

My primary NAS also connects directly to a RT-AX86U LAN jack. and it reports:
Advertised link modes:
10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full

Thinking that the issue may be the cable, or the router LAN jack, I exchanged positions between the two, but the poor connection to the backup NAS remained, while the primary NAS, continued to perform as expected.

Any ideas on what is happening here? Thanks!

 

[ColinTaylor]

Fault with the Ethernet socket on the backup NAS?

 

[_zero]

Thanks! I overlooked that. I'll break down the unit and look to see if there is a easy swap or diagnosis.

My short term replacement is a 14 TB Easystore, which as a backup device seems as a possible candidate if a simple fix isn't available.