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Cheat sheet

CCNA Cheat Sheet

Practice this exam

Network Fundamentals

  • 20% of exam
  • Fundamentals IPv4 TCP vs UDP OSI Stack

Network Access

  • 20% of exam
  • Switching VLAN + STP Trunk vs Access Switching Picker

IP Connectivity

  • 25% of exam
  • Routing OSPF + FHRP Routing Picker Static vs OSPF

IP Services

  • 10% of exam
  • IP Services Connectivity Triage NAT vs DHCP Private IPv4

Security + Automation

  • 25% of exam
  • Security Automation ACL vs NAT Router vs Switch

Quick Facts

  • Exam 200-301
  • Time 120 min
  • Level Associate
  • Vendor Cisco
  • Core Networking
  • Score Varies
  • Skill Troubleshoot path

OSI Stack FU

  • Physical -> Data -> Network -> Transport
  • L1: bits L2: frames L3: packets L4: segments

TCP vs UDP FU

TCP

  • Reliable
  • Sequenced
  • Connection

UDP

  • Fast
  • No handshake
  • Best effort
  • Reliable vs fast

Fundamentals FU

  • LAN Local network
  • WAN Remote network
  • Router Layer 3 forwarding
  • Switch Layer 2 forwarding
  • MAC Layer 2 address
  • IP Layer 3 address

IPv4 FU

  • /24 256 addresses
  • /25 128 addresses
  • /26 64 addresses
  • /27 32 addresses
  • /28 16 addresses
  • Gateway Off-subnet exit
  • Broadcast Last address
  • Network First address

Trunk vs Access AC

Trunk

  • Many VLANs
  • 802.1Q tags
  • Switch links

Access

  • One VLAN
  • Untagged user
  • Endpoint links
  • Many vs one

Switching Picker AC

  • One VLAN → Access port
  • Many VLANs → Trunk
  • Loop risk → STP
  • More bandwidth → EtherChannel
  • MAC limit → Port security
  • Gateway VLAN → SVI

Switching AC

  • CAM table MAC lookup
  • Flood Unknown unicast
  • VLAN Broadcast domain
  • Trunk Multi-VLAN link
  • 802.1Q VLAN tag
  • EtherChannel Bundled links

VLAN + STP AC

  • Access port One VLAN
  • Native VLAN Untagged trunk
  • Root bridge STP center
  • Root port Best root path
  • Designated Segment forwarder
  • Blocking Loop prevention

Wireless AC

  • SSID Network name
  • BSSID AP radio MAC
  • WLC AP controller
  • CAPWAP AP tunnel
  • WPA2 Wireless security
  • Roaming AP handoff

Route Choice CO

  • Longest match -> AD -> metric
  • Specific first Trust second Cost third Gateway last

Static vs OSPF CO

Static

  • Manual
  • Small networks
  • No updates

OSPF

  • Dynamic
  • Link state
  • Metric cost
  • Manual vs learned

Routing Picker CO

  • Manual path → Static
  • Unknown path → Default
  • Dynamic LAN → OSPF
  • Backup gateway → FHRP
  • Specific route → Longest match
  • Route choice → AD then metric

Routing CO

  • Connected Direct route
  • Static Manual route
  • Default Gateway route
  • AD Trust value
  • Metric Path cost
  • Longest match Most specific

OSPF + FHRP CO

  • OSPF Link-state routing
  • Area 0 Backbone area
  • Neighbor Adjacency peer
  • Cost OSPF metric
  • DR/BDR Multiaccess roles
  • FHRP Gateway redundancy

Private IPv4 SE

  • 10 | 172.16-31 | 192.168
  • Class A Class B range Class C Needs NAT

Connectivity Triage SE

  • No link → Check cable
  • No IP → Check DHCP
  • Wrong subnet → Check mask
  • Off subnet fails → Check gateway
  • Name fails → Check DNS
  • Route missing → Check table

IP Services SE

  • DHCP Address leasing
  • DNS Name resolution
  • NTP Time sync
  • NAT Address translation
  • PAT Port overload
  • SNMP Device monitoring
  • Syslog Event messages
  • QoS Traffic priority

Router vs Switch SE

Router

  • Layer 3
  • Routes packets
  • Between networks

Switch

  • Layer 2
  • Forwards frames
  • Inside LAN
  • Network vs LAN

Security SE

  • ACL Traffic filter
  • AAA Access services
  • SSH Secure CLI
  • Port security MAC limiting
  • DHCP snooping Rogue DHCP block
  • DAI ARP protection

ACL vs NAT SE

ACL

  • Filters traffic
  • Permit/deny
  • Security

NAT

  • Translates addresses
  • Inside/outside
  • Reachability
  • Filter vs translate

Automation SE

  • JSON Data format
  • REST API style
  • Controller Central brain
  • Overlay Logical network
  • Underlay Physical transport
  • Ansible Config automation

Common Traps

Layer mixup

  • Switch uses MAC ≠ Router uses IP

Port mixup

  • Access is endpoint ≠ Trunk is multi-VLAN

Route choice

  • Longest match wins ≠ Metric is later

NAT confusion

  • NAT translates ≠ ACL filters

DHCP confusion

  • DHCP gives IP ≠ DNS gives name

Last Minute

  • 1. Weights: 20 / 20 / 25 / 10 / 25
  • 2. Switch = MAC forwarding
  • 3. Router = IP forwarding
  • 4. Trunk carries many VLANs
  • 5. Access carries one VLAN
  • 6. Longest match first
  • 7. AD before metric
  • 8. DHCP leases addresses
  • 9. DNS resolves names
  • 10. ACL filters traffic