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1.1 Network components & their OSI layer
- Router = L3, routes between networks. Switch = L2 (L3 switch can route). NGFW/IPS = security at L3-L7. AP = wireless L1/L2. WLC = controls many APs.
- PoE delivers power over the Ethernet cable to APs/phones/cameras.
PoE standards (memorize the wattages) | Standard | Name | Power |
|---|
| 802.3af | PoE | 15.4 W |
| 802.3at | PoE+ | 30 W |
| 802.3bt Type 3 | PoE++ | 60 W |
| 802.3bt Type 4 | PoE++ | 90 W |
| Cisco UPOE | proprietary | 60 W |
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1.2 Topology architectures
- Two-tier (collapsed core) = access + collapsed core/distribution. Three-tier = access → distribution → core (large campus).
- Spine-leaf = every leaf connects to every spine, leaves never connect to leaves; optimized for east-west (data-center) traffic.
- SOHO = small office/home office. On-prem (capex, you own it) vs cloud (opex, you rent it).
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1.3 Physical interfaces & cabling
- Single-mode fiber: laser, narrow core, long distance (km). Multimode fiber: LED/VCSEL, wider core, shorter runs. Copper (UTP): ~100 m max.
- Point-to-point vs shared media. Know connector/transceiver basics (SFP).
04
1.5 TCP vs UDP & well-known ports
- TCP = connection-oriented: 3-way handshake (SYN, SYN-ACK, ACK), sequencing, acknowledgements, retransmission, flow control. Reliable but heavier.
- UDP = connectionless, best-effort, no handshake. Lower overhead - used for voice/video/DNS queries.
Well-known ports (high-yield) | Port | Proto | Service |
|---|
| 20/21 | TCP | FTP data/control |
| 22 | TCP | SSH |
| 23 | TCP | Telnet |
| 25 | TCP | SMTP |
| 53 | UDP/TCP | DNS |
| 67/68 | UDP | DHCP server/client |
| 69 | UDP | TFTP |
| 80 | TCP | HTTP |
| 443 | TCP | HTTPS |
| 123 | UDP | NTP |
| 161/162 | UDP | SNMP poll/trap |
| 514 | UDP | Syslog |
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1.11 Wireless principles
- 2.4 GHz non-overlapping channels: 1, 6, 11. 5 GHz has many more channels.
- SSID is the network NAME, not security. Encryption comes from WPA2/WPA3.
- AP modes and RF basics: coverage vs capacity, interference.
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1.12 Virtualization fundamentals
- Hypervisor runs VMs, each with a full guest OS. Containers share the host kernel (lighter, faster).
- VRF = multiple independent L3 routing tables on one router (virtual routers).
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1.13 Switching concepts
- A switch learns MACs from the SOURCE MAC of incoming frames and builds the MAC address table (default aging 300 s).
- Forwarding: known unicast → out the one correct port. Unknown unicast / broadcast → flooded out all ports except the one it arrived on.
- Frame switching is done in hardware (ASIC).