Sefism Network Engineering Cheat Sheet

What this cheat sheet is

The network engineering cheat sheet is the revision companion to Sefism's Network engineering roadmap. It is for students and early-career engineers becoming network engineers, and it runs from the OSI model and subnetting to switching, routing, security, wireless, automation and cloud networks.

Use it to revise each idea in a line or two, check the Cisco IOS command you need and spot the classic mistake before you make it on a real network. Most concepts include a command block, so the sheet doubles as a quick CLI reference while you build labs.

Three editions, one per path

The sheet follows the roadmap's path choice:

• Enterprise (Cisco) (the default): every command is Cisco IOS or IOS XE, the syntax you type in labs and in a first job. 72 concepts.
• Cloud networking: the same routing, subnetting and security basics, then VPCs, route tables, security groups, hybrid VPNs and network code. Commands are Cisco IOS for labs and the AWS CLI for the cloud. 74 concepts.
• Network security: routing and switching first, then ACLs, stateful and next-generation firewalls, VPNs, segmentation and the Layer 2 attacks switches can stop. Commands are Cisco IOS, with firewall ideas that carry to any vendor. 75 concepts.

All three editions have the same ten chapters.

Chapter by chapter

1. Models, addressing and subnetting (10 concepts)

The OSI and TCP/IP models, TCP versus UDP, common port numbers, IPv4 addresses and CIDR prefixes, a subnetting table, VLSM, IPv6 addressing, ARP, DHCP and DHCP relay, and DNS records.

2. Switching and VLANs (8 concepts)

The MAC address table, VLANs, trunks and 802.1Q, inter-VLAN routing, Spanning Tree Protocol, PortFast, BPDU Guard and Root Guard, EtherChannel and LACP, and CDP and LLDP. Every entry has IOS commands.

3. Routing: static, OSPF and BGP (9 concepts)

The routing table, longest prefix match, administrative distance and metric, static and default routes, OSPF, OSPF network types and DR/BDR, BGP basics, a routing protocol comparison, and first hop redundancy with HSRP and VRRP.

4. Labs, the CLI and troubleshooting tools (7 concepts)

Cisco Packet Tracer, GNS3, Cisco Modeling Labs Free, IOS command modes, everyday show commands, ping, extended ping and traceroute, and packet capture.

5. Certification plan

The CCNA 200-301, the exam topics blueprint, CompTIA Network+, and spaced repetition and practice exams, with cloud networking or network security certifications on those editions. The chapter covers what the CCNA tests now and after the refresh the sheet expects in February 2027.

6. Network security: ACLs, firewalls and VPNs

Access control lists, NAT and PAT, port security, DHCP snooping and Dynamic ARP Inspection, AAA with TACACS+ and RADIUS, device hardening and SSH, stateful firewalls and zones, and IPsec site-to-site and remote access VPNs. The network security edition adds next-generation firewalls and IPS, and segmentation and zero trust.

7. Wireless networking (5 concepts)

Wi-Fi standards, bands and channels, access points and controllers, WPA2, WPA3 and 802.1X, and RF, interference and site surveys.

8. Network automation and monitoring (7 concepts)

Python with Netmiko, JSON and YAML, REST APIs, RESTCONF and NETCONF, Ansible for networks, SNMP, syslog and severity levels, and configuration backups and drift.

9. Cloud networking

VPCs and VNets, subnets and route tables, security groups and network ACLs, internet and NAT gateways, peering and transit hubs, hybrid connectivity, private endpoints and flow logs, with network infrastructure as code on the cloud edition.

10. Your first network role (6 concepts)

The NOC engineer role, tickets, priorities and SLAs, structured troubleshooting, change management and maintenance windows, network documentation, and runbooks and escalation.

Each chapter lists up to three library resources, including Cisco Networking Academy, Jeremy's IT Lab: CCNA 200-301 Complete Course, GNS3, OPNsense, Netmiko and the Amazon VPC User Guide.

Rules of thumb and glossary

Each edition has eight rules of thumb: seven shared and one for its path. The shared ones include: subnet on paper every day for two weeks until a /27 or /29 takes under ten seconds; look before you touch and save show output before any change; always test the return path; copy running-config to startup-config only after testing; keep every lab as saved configs in Git; and name the layer in every fault note. The path rules cover IOS shortcuts (enterprise), non-overlapping address ranges (cloud) and giving every firewall rule an owner, a reason and a review date (security).

A glossary of 62 short terms sits alongside, and every concept joins it automatically.

How to use it with the roadmap

• After each stage, read the chapter and type its commands into your lab from memory, then check. Roadmap topics link straight to the concepts that cover them.
• While building labs, keep chapters 2, 3 and 4 open. The show commands and troubleshooting tools turn guesses into evidence.
• Before the CCNA or a technical round, reread subnetting, routing and security, and practise explaining one of your labs in two minutes, as the roadmap's last stage suggests.

How it works on Sefism

Everything on Sefism is free to learn from. The public page shows all ten chapters with their introductions and opens the first two in full. Keeping the sheet uses credits and opens every chapter in the member area; new members get starting credits when they join. Adding the Network engineering roadmap to your dashboard (your first roadmap is free) brings this sheet with it.

Related on Sefism

• Is the CCNA still worth it for a fresh graduate?
• How to move from NOC to network engineer
• Network Configuration Backup and Drift Detection for University Campus Networks, a project built on chapter 8.
• The Cybersecurity cheat sheet and Cloud engineering cheat sheet for the wider security and cloud picture.

FAQ

Is this a CCNA cheat sheet? It covers the CCNA ground in the roadmap's order with IOS commands, but it is a revision aid, not an exam guide. Use the official blueprint for the exam itself.

Does it include a subnetting cheat sheet? Yes. The first chapter has a subnetting table, VLSM and the CIDR entries.

Which edition should I pick? Enterprise for Cisco and the CCNA, cloud networking if your target jobs mention VPCs and hybrid links, network security if they ask for firewalls and VPNs.

Can I use it with Packet Tracer? Yes. The roadmap treats Packet Tracer as enough for most of the CCNA, and the labs chapter covers GNS3 and Cisco Modeling Labs Free for the rest.