Network engineering cheat sheet (Enterprise (Cisco))

1. 1Models, addressing and subnettingHow data moves through the layers, the ports you will see every day, IPv4 and IPv6 addressing, and the subnetting maths every other stage depends on.10 concepts

   1. 1OSI and TCP/IP modelsTwo ways to split networking into layers.
   2. 2TCP vs UDPThe two main transport protocols.
   3. 3Common port numbersThe numbers that identify a service on a host.
   4. 4IPv4 addresses and CIDR prefixesAn IPv4 address is 32 bits written as four numbers from 0 to 255.
   5. 5Subnetting tableThe prefixes you meet most, with their masks, block sizes and usable hosts.
   6. 6VLSMCarving one block into subnets of different sizes, largest first, so each LAN, link and loopback gets only the addresses it needs.
   7. 7IPv6 addressingIPv6 addresses are 128 bits written in hex groups, such as 2001:db8:10::1/64.
   8. 8ARPThe IPv4 protocol that finds the MAC address for an IP address on the local network by broadcasting a question and caching the answer.
   9. 9DHCP and DHCP relayDHCP hands clients an address, mask, gateway and DNS servers through Discover, Offer, Request, Acknowledge.
   10. 10DNS recordsDNS turns names into addresses.

   10 in this chapterOpen this chapter
2. 2Switching and VLANsHow switches learn and forward frames, how VLANs and trunks split one physical network into many, and the loop protection that keeps a campus network alive.8 concepts

   1. 1MAC address tableThe switch table mapping each MAC address to the port it was last seen on.
   2. 2VLANA VLAN splits one switch, or many, into separate Layer 2 networks.
   3. 3Trunks and 802.1QA trunk carries many VLANs over one link by adding a 4-byte 802.1Q tag with the VLAN number to each frame.
   4. 4Inter-VLAN routingHosts in different VLANs need a router to talk.
   5. 5Spanning Tree ProtocolSTP stops loops in a switched network by electing a root bridge and blocking redundant paths.
   6. 6PortFast, BPDU Guard and Root GuardPortFast puts an access port straight into forwarding.
   7. 7EtherChannel and LACPBundling several physical links into one logical link.
   8. 8CDP and LLDPDiscovery protocols that let directly connected devices announce their name, model, port and address.

   8 in this chapterOpen this chapter
3. Routing: static, OSPF and BGPHow a router chooses where a packet goes, static and default routes, OSPF inside an organisation, BGP between organisations, and gateway redundancy.9 conceptsOpens with credits
4. Labs, the CLI and troubleshooting toolsThe simulators and emulators you practise on, how the Cisco command line is organised, and the show, ping, traceroute and capture tools that turn guesses into evidence.7 conceptsOpens with credits
5. Certification planWhat the CCNA exam covers now and after its February 2027 refresh, where other certifications fit, and how to turn a blueprint into a study plan you finish.4 conceptsOpens with credits
6. Network security: ACLs, firewalls and VPNsFiltering traffic with ACLs, translating addresses, locking down switch ports and device access, stateful firewalls and the VPNs that join sites and users.8 conceptsOpens with credits
7. Wireless networkingWi-Fi standards, bands and channels, how controllers manage access points, the security protocols to choose and why wireless problems are so often radio problems.5 conceptsOpens with credits
8. Network automation and monitoringPython and Ansible for repeatable changes, APIs and structured data, and the SNMP, syslog and backups that tell you what the network is doing.7 conceptsOpens with credits
9. Cloud networkingVirtual networks in the cloud: address plans, route tables, gateways, security groups, joining networks together and to the office, and the logs that show what flowed.8 conceptsOpens with credits
10. Your first network roleWhat NOC and junior network jobs look like day to day: tickets, escalation, change windows, a troubleshooting method and the documentation that makes you trusted.6 conceptsOpens with credits
11. 11Glossary, A to ZEvery concept in the sheet and the smaller terms it uses, in one list.134 terms

Routing, switching, CCNA, cloud networks.