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, iptables
  Security:
  Integrity, Hashing (SHA256, MD5, Argon2), MAC, HMAC, Digital Signatures(RSA, DSA, ECDSA)
  Encryption: Symmetric vs Asymetric Key, Symmetric Key Algos (AES, DES), Asymmetric Key Algos(DH, RSA, EC(ECDH, secp256k1))
  Build Libraries: Botan, Openssl(build on x86, Cross Compile on ARM)
  Threat Modelling: STRIDE framework
  DevSecOps STRIDE framework
  VPN: What, VPN Tunnel: IKEv1, IKEv2, IPSec(Modes(tunnel, transport), Headers(AH, ESP)), Terms( DPD(Dead Peer Detection), Nonce, PFS(Perfact Forward Secrecy), SA(Security Association), SA, SAD, SPI), Packet Flow(Inbound, Outbound), VPN NAT Traversal

Layer-6(Presentation)
  SSL/TLS:
  SSL vs TLS, NSS, mkcert, Terms(SNI), Let's Encrypt Root CA
  TLS Client Server Certification Exchange

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)
  Authentication Procotols: Kerberos, OAuth, OIDC(OpenID Connect), SAML
  MCP(Model Context Protocol)
  REST API
  WebServers: Apache, Ngnix
  Load testing Tools
  RBI(Remote Browser Isolation)
  HTTP:
  Introduction( Methods(GET,POST,PUT,DELETE)), Headers, Cookies(Session, Domain, Stolen Cookie, Cookie Surrogate)
  Authentication: Authenticate by IDP:Get session cookie, Cookies(Session, Domain, Global, Stolen), JWT Token, Refresh Token, HTTP Connect