Computer Networking Masterclass: Interview Success

Explore layer two switches and mac addresses, including how switches forward data using mac addresses, vlans, quality of service, and port mirroring to improve lan performance and security.

Explore how a plug-and-play switch forwards frames based on destination Mac addresses. Observe how the switch floods frames when entries are missing and uses aging, static, or dynamic tables.

Learn how Ethernet headers frame data by carrying destination and source MAC addresses, Ethertype, optional Vlan tag, and a trailer with FCS, guiding payload processing up to 1500 bytes.

Learn how arp maps an ip address to a mac address on the same network, builds arp tables, and uses broadcast requests and replies to resolve addresses.

Master switchport modes such as access, trunk, dynamic auto, dynamic desirable, VLAN only, and general mode. Learn how VLAN tagging enables multiple VLANs on trunk ports.

learn vlan trunking protocol (VTP) for vlan information sharing across switches in a Cisco environment, including server, http client, and transparent modes, plus http advertisements and revision numbers.

Review how the root path cost is calculated from link speeds and how the lowest cost path is chosen via BPDU-driven topology updates in STP.

Explore IPv6, a 128-bit addressing scheme that addresses IPv4 shortages and improves routing and security, with the fixed 40-byte header and fields like traffic class and flow label.

Learn how a network gateway bridges two networks, enables cross-network communication, and how devices configure the gateway IP address as their default gateway to forward outbound traffic.

Understand how routers use a routing table to determine the best path for forwarding packets, including directly connected and remote networks, via next hop or interface, with continuous updates.

Configure static routing by manually populating a router's table with destination networks and next-hop addresses for small networks, and plan for restoration or reconfiguration when links fail.

Compare static and dynamic routing, showing manual configuration versus automatic updates, how each scales, their convergence times, configuration complexity, bandwidth impact, and redundancy options.

Explore backup routes as a secondary path that preserves traffic when the primary path fails, and configure static routes and backup interfaces with OSPF or EGP, plus equal-cost multipath.

Understand layer three switches that combine switching and routing to move traffic between subnets, operate at layer two and layer three, support ACLs, QoS, and OSPF/BGP in enterprises, reducing costs.

Routing moves data between different networks using IP, BGP, and OSPF to determine the best path, while switching moves data within a network or VLAN using MAC addresses.

NAT translates private IP addresses to public IP addresses for internet access, using static and dynamic NAT, NAT overload, and NAT66/NAT64 for IPv6 translation.

Compare Nat and Pat and explain static versus dynamic mappings for private to public addresses. Explain port forwarding, its rules, and how double Nat creates challenges for apps and troubleshooting.

Explain how OSPF builds a link-state topology database and computes shortest paths, detailing packet types (hello, db, lsr, lsu, ack), multicast addresses, and hello and dead timers.

Explore OSPF area types, including backbone area and stub areas, and how ABRs generate default routes and stub router LSAs to limit external LSAs.

Learn the border gateway protocol (BGP), an inter-domain routing protocol using a path vector to exchange routes between autonomous systems, with eBGP and iBGP and policy based routing.

Explore BGP message types—open, update, notification, keepalive, and router refresh—and learn key attributes like S path, next hop, origin, local preference, med, and community that guide path selection.

Explore how BGP routers exchange routes through peering over TCP port 179 and use update messages, open messages, and keepalive to advertise or withdraw routes and select the best path.

Set the maximum transmission unit, the largest packet size without fragmentation, for each network. Use jumbo frames where supported and path MTU discovery to prevent VPN connectivity issues.

The transport layer enables app-to-app communication using source and destination ports. It uses tcp or udp and ports 0 to 65,535 divided into 0–1023, 1024–49,151, and dynamic or private.

Explore how tcp ensures reliable, ordered, connection-oriented delivery over ip networks, highlighting header fields such as source and destination ports, sequence and acknowledgement numbers, and window size.

Learn how tcp uses acknowledgements, retransmissions, and error detection to ensure reliable data delivery in correct order. See how sequence numbers and the receiver acknowledges the next expected sequence number.

Master TCP flow control and congestion control using the sliding window and advertised window size to regulate sender rate and respond to packet loss, delay, and ECN echo flags.

Learn how tcp terminates connections with a four-way handshake to gracefully close using a fin exchange, and contrast it with an abrupt termination via a tcp reset packet.

Explain how TCP retransmissions preserve reliability by using acknowledgments and retransmission timeout to trigger resends. Demonstrate fast retransmit with three duplicate acks and selective retransmission to target only lost segments.

Understand how the TCP three-way handshake establishes a connection between sender and receiver, negotiating sequence numbers, window size, MSS, and key TCP options.

Explore UDP, a connectionless and unreliable transport protocol in the TCP/IP suite, enabling fast, stateless datagram transmission with an eight-byte header and broadcast and multicast support.

Explore how UDP operates as a connectionless, unreliable transport with a four-field header and independent datagrams. Its low overhead supports real-time use like streaming and online gaming.

Explore QUIC, Google's transport protocol built on UDP, to deliver low latency, reliable, and secure web traffic for real-time apps and mobile networks, avoiding TCP connection setup delays.

Discover how multiplexing in quic transmits multiple streams over a single connection, using unique stream IDs and prioritization to reduce head-of-line blocking and improve latency and efficiency.

Discover how QUIC underpins HTTP/3 as the transport, delivering reliable, encrypted communication with TLS 1.3, multiplexed streams, and interoperable standards via the IETF.

Discover port numbers for common services, such as http/https on 80 and 443 and ftp on 21/20, along with dns 53 and dhcp 67/68.

Discover how emesis, or maximum segment size, governs how much data fits in a tcp segment, and how path mtu discovery and fragmentation affect performance.

Compare M2 and RMS to grasp how the maximum packet size and TCP payload vary across data link, network, and transport layers, including fragmentation and the TCP handshake.

Explore the application layer as the interface between software and network, enabling email, web, file transfer, remote login with data formatting, encryption and decryption, authentication, authorization, error handling, and compression.

Explore how the http protocol enables client–server web communication via a request–response cycle. Identify common http methods like get, post, put, delete, head, options, and batch.

Explore how http enables the web via a client-server request-response cycle, using methods such as get, post, put, delete, head, options, and batch to exchange html, images, and videos.

Explore http headers and status codes, including content type, content length, user agent, and host, and common 1xx–5xx ranges, plus http2 and http3 based on Quic to boost performance.

Compare http/2 and http/3 on connection establishment, security, and performance, noting http/3's quic handshake, zero round-trip connections for reconnects, and encryption by default.

Compare http/2 and http/3 to show connection setup, reliability, and security differences, including QUIC and TLS 1.3; http/2 suits networks, http/3 excels in low latency and zero round trip time.

Explore the dns, a hierarchical, distributed, and scalable system that translates domain names to ip addresses, from root to tld and sld levels, including subdomains like blog.example.com.

Explore the DNS resolution process, detailing recursive lookup through root, TLD, and authoritative servers to obtain and cache an IP address for the client, and contrast it with iterative resolution.

Explore how DNS records store and manage domain-name information, including A, Quad, CNAME, MX, TXT, and NS records, and how caching on resolvers and authoritative servers speeds up resolution.

Master DHCP basics to automatically assign IP addresses and network configuration parameters via a client-server model, manage leases and renewals, and decide when to use DHCP versus static IPs.

Explore the DHCP four-step IP address assignment—discover, offer, request, and ack—and how relay agents forward messages, including unicast discovery in relay scenarios and the IPv6 DHCP extension for configuration.

Trace a ping from source to destination, detailing ICMP echo request and reply, and how ARP and DNS resolution enable MAC addresses in the switch table and frame delivery.

Trace how a browser resolves a domain to an IP address, then opens a TCP connection on port 80 or 443 and completes a TLS handshake for secure HTTP.

Agree on a troubleshooting plan, then ask open-ended follow-up questions and troubleshoot layer by layer from physical to application using tools like cable testers, ping, traceroute, ipconfig, nslookup, and curl.

Explore firewall types from packet filtering at the network layer to stateless checks, and progress to stateful, proxy, and next-gen firewalls with deep packet inspection, intrusion prevention, and application awareness.

Discover how vpn creates a secure, encrypted tunnel over public networks to connect devices to a vpn server, masking ip addresses and supporting site-to-site or remote access connections.

Explore how NAT traversal enables VPN connections behind routers and firewalls, featuring UDP hole punching, IPsec NAT, and perfect forward secrecy; compare split tunneling and OpenVPN versus IPsec.

Learn how load balancers distribute traffic across servers to optimize resources and boost availability. Explore hardware versus software options, health checks, session persistence, SSL termination, and content-based routing.

Explore how load balancing algorithms distribute traffic across multiple servers, covering round robin, least connections, IP hash, weighted round robin, weighted least connections, and response-time strategies.

Explore application load balancers (albs) at layer seven, enabling HTTP/HTTPS content-based routing with path-based and host-based routing, SSL termination, and sticky sessions for microservices across AWS, Azure, and Google Cloud.

Explore internal load balancers for private network traffic between microservices and databases, and DNS-based load balancers for latency-aware global routing across AWS, Azure, and Google Cloud.

Analyze strategies to optimize network performance across speed, reliability, capacity, and security, and identify metrics that affect performance in each area for senior-level interview success.

Continual monitoring sustains resilient networks with real time insights from monitoring tools, telemetry, and observability. Identify bottlenecks using flow logs, routing tables, and application latency to optimize performance.

Improve network performance across layer one and layer two by optimizing physical hardware, high quality cables and grounding, plus switches, VLANs, QoS, and redundancy protocols.

Optimize the application layer to boost performance through code improvements and caching. Apply cross-layer strategies, monitoring, quality of service, and security to support horizontal scaling and resilient networks.

Learn to optimize 4K video uploads to SSD storage over a sand network by assessing bottlenecks and upgrading bandwidth with QoS, VLANs, and RAID 10.

Explore core network performance tools like ping, traceroute, and MTR to measure latency, packet loss, and path quality, then diagnose with Wireshark, iperf, and Speedtest CLI.