N750 - slow LAN data transmission

Hello, I have a problem with speed during data transmission on LAN between WD My book and NAS Synology. The transfer speed is only 2,5MB/s! Router support 1Gb, so where could be a problem? Thanks for your help.

I have checked ethernet speed and it support only 100MB/s! How WD can present that this router support 1GB when the reality is different?! There is missing Hardware (chip) for NAT support (Western Digital My Net N750 [Old OpenWrt Wiki]).