Wired LAN between main router and AiMesh node stay at 100 Mbps

Hi,
I have just added my first AiMesh node:
Main AiMesh : RT-AC68U ( AP mode )
Second Aimesh : RT-AC67U

All seems to work wells, but I have have noticed that the wired link between this two AiMesh node stay at 100 Mbps ! Should not it be at 1Gbps?
The link is from LAN1 port on the first node to the WAN port on the second one.

View attachment 21445
View attachment 21446