Ask HN: Recommendation for Networks Refresher

I feel like I've learnt about networking / TCPIP / DNS multiple times over the last 30 years and it never seems to stick. After a long support call with a cloud vendor today I feel like I need to relearn from first principals. Any suggestions for online books / youtube channels etc. I'm currently focused on private networking in the cloud environment but feel I need to improve my base knowledge. I'm even considering certification to force myself to retain some of this information!