Duties, Protocols of Each Layer
Layer-2: hub router switch bridge, Ping from Host-1 to Host-2
Layer-2.5
  MPLS
Layer-3
  Protocols: IP
  Security: HMAC, MAC, Signing, Integrity, Build Libraries(Botan, Openssl)
  iptables
Layer-6(Presentation)
  SSL_TLS: TLS, SSL, TLS vs SSL, NSS(TLS Implementation) vs Openssl
  mkcert(Local Self Signed CA(for dev testing))
  Terms: SNI
  Let's Encrypt Get cert signed by Let's Encrypt Root CA
Layer-7(Application)
  DNS: Introduction(Name resolution, Forward, Reverse lookup, Terms), DNS Records(A, AAAA, Alias, CAA, CNAME, MX, PTR, RR, SOA, SPF, TXT)
  gRPC: Introduction(gRPC, gRPC vs REST), Code(golang gRPC server & client)
  HTTP: Features, Adv, Disadv, Methods(GET,POST,PUT,DELETE), Header, Cookie
  REST API
  WebServers: Apache, Ngnix
  Kerberos
  OAuth
  RBI(Remote Browser Isolation)