Network Fundamentals
20%of exam
Network Access
20%of exam
IP Connectivity
25%of exam
IP Services
10%of exam
Security + Automation
25%of exam
Quick Facts
- Exam
- 200-301
- Time
- 120 min
- Level
- Associate
- Vendor
- Cisco
- Core
- Networking
- Score
- Varies
- Skill
- Troubleshoot path
OSI Stack
Physical -> Data -> Network -> Transport
L1: bitsL2: framesL3: packetsL4: segments
TCP vs UDP
TCP
- Reliable
- Sequenced
- Connection
UDP
- Fast
- No handshake
- Best effort
Reliable vs fast
Fundamentals
- LAN
- Local network
- WAN
- Remote network
- Router
- Layer 3 forwarding
- Switch
- Layer 2 forwarding
- MAC
- Layer 2 address
- IP
- Layer 3 address
IPv4
- /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
Trunk
- Many VLANs
- 802.1Q tags
- Switch links
Access
- One VLAN
- Untagged user
- Endpoint links
Many vs one
Switching Picker
- One VLAN→Access port
- Many VLANs→Trunk
- Loop risk→STP
- More bandwidth→EtherChannel
- MAC limit→Port security
- Gateway VLAN→SVI
Switching
- CAM table
- MAC lookup
- Flood
- Unknown unicast
- VLAN
- Broadcast domain
- Trunk
- Multi-VLAN link
- 802.1Q
- VLAN tag
- EtherChannel
- Bundled links
VLAN + STP
- Access port
- One VLAN
- Native VLAN
- Untagged trunk
- Root bridge
- STP center
- Root port
- Best root path
- Designated
- Segment forwarder
- Blocking
- Loop prevention
Wireless
- SSID
- Network name
- BSSID
- AP radio MAC
- WLC
- AP controller
- CAPWAP
- AP tunnel
- WPA2
- Wireless security
- Roaming
- AP handoff
Route Choice
Longest match -> AD -> metric
Specific firstTrust secondCost thirdGateway last
Static vs OSPF
Static
- Manual
- Small networks
- No updates
OSPF
- Dynamic
- Link state
- Metric cost
Manual vs learned
Routing Picker
- Manual path→Static
- Unknown path→Default
- Dynamic LAN→OSPF
- Backup gateway→FHRP
- Specific route→Longest match
- Route choice→AD then metric
Routing
- Connected
- Direct route
- Static
- Manual route
- Default
- Gateway route
- AD
- Trust value
- Metric
- Path cost
- Longest match
- Most specific
OSPF + FHRP
- OSPF
- Link-state routing
- Area 0
- Backbone area
- Neighbor
- Adjacency peer
- Cost
- OSPF metric
- DR/BDR
- Multiaccess roles
- FHRP
- Gateway redundancy
Private IPv4
10 | 172.16-31 | 192.168
Class AClass B rangeClass CNeeds NAT
Connectivity Triage
- 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
- 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
Router
- Layer 3
- Routes packets
- Between networks
Switch
- Layer 2
- Forwards frames
- Inside LAN
Network vs LAN
Security
- ACL
- Traffic filter
- AAA
- Access services
- SSH
- Secure CLI
- Port security
- MAC limiting
- DHCP snooping
- Rogue DHCP block
- DAI
- ARP protection
ACL vs NAT
ACL
- Filters traffic
- Permit/deny
- Security
NAT
- Translates addresses
- Inside/outside
- Reachability
Filter vs translate
Automation
- 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
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