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+# CCNA Quick Reference Notes
+
+- Computer Network: Digital Telecommunications network that allows nodes to share resources
+- Switches: Layer 2 devices that with many ports that connect hosts on a LAN.
+- Router: Layer 3 devices that have fewer ports and connects LANs together.
+- Ethernet: A collection of network protocols and standards
+- Ethernet standards: IEEE 802.3 (1983)
+    - 10Mbps Ethernet: 802.3i 10BASE-T 100m
+    - 100Mbps Fast Ethernet: 802.3u 100BASE-T 100m
+    - 1000Mbps Gig. Ethernet: 802.3ab 1000BASE-T 100m
+    - 10Gbps 10 Gig. Ethernet: 802.3an 10GBASE-T 100m
+- PCs - Transport (TX) data on pins one and two.
+- Switches - Recieve (RX) data on pins one and two.
+- PCs - RX on pins three and six.
+- Switches - TX on three and six.
+- Fiber Optic Connections: IEEE 802.3.ae
+- Single mode:
+    - Narrower than multimode
+    - Light enters at a single angle from a laser based transmitter.
+    - Allows longer cables then UTP and multimode fiber.
+    - More expensive then multimode.
+- Multimode fiber:
+    - Wider than single mode.
+    - Allows multiple light waves to enter the core.
+    - Allows longer cables than UTP but shorter than single mode.
+    - Cheaper than single mode being LED-based.
+- Fiber Optic Standards:
+    - 1000BASE-LX 802.3Z 1Gbps multi/single 5km single
+    - 10GBASE-SR 802.3ae 10Gbps multi 400km
+    - 10GBASE-LR 802.3ae 10Gbps single 10kilo
+    - 10GBASE-ER 802.3ae 10Gbps single 30kilo
+
+## OSI Model
+
+Application
+Presentation
+Session
+Transport
+Network
+Data Link
+Physical
+
+MAC Address: 6 bytes (48-bits)
+
+## VLANs
+
+- A LAN is a single broadcast domain.
+- A broadcast domain is a group of devices which will receieve a broadcast frame. (Destination MAC: FFFFF:FFFFF:FFFFF)
+- Lots of unnecessary broadcasts traffice can reduce network performance
+
+### What is a VLAN?
+
+- Logically seperates end-hosts at Layer 2.
+- Are configured on Layer 2 switches on a per-interface bases.
+- Any end host connected to that interface is part of the VLAN.
+
+### Configuring a VLAN
+
+- `# sh vlan br`
+- `# switchport mode access`
+
+An access port is a port is a port that belongs to a single VLAN, untagged port.
+
+Switchports that carry multiple VLANs are called trunk ports, tagged ports.
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